What I think many responding here either miss or are having trouble to conceive is the fact that you are facing an aggressive group that you cannot ignore. These kind of people are not only pushy, but nosey, and won't let you be no matter how hard you try. These kinds of circumstances are of the type anticipated by the school I follow, Nichiren Buddhism, and part of the reason why Nichiren directed us to only teach the Lotus Sutra in the degenerate age. There is, however, some general advice I think I can offer regardless of the sect you adhere to.
Individuals like these Christians can be dangerous. If you offend them, you may have property damaged, be harmed physically, or find yourself facing false accusations with legal consequences, not to mention petty rumors. They will excuse their consciences of any wrongdoing they commit for their religion. They are not like Buddhists and do not feel any sense of obligation to be reasonable with, or compassionate to, those who are not of their own faith or who oppose it. If you confront them in any way, expect to stand out, and to stand for Buddhism.
It seems like you're already doing your best to ignore them and that you don't want to simply give in and let others control your life. If you find that you can't remain silent, your best option is to engage them firmly in polite debate. This will challenge you to learn more about Buddhadharma and to appreciate the profundity of its teaching in comparison with that of other religions. When you point out the weaknesses and absurdities of the Christian religions and other Abrahamic faiths, always assert the correctness of the Buddha's teaching and offer them the opportunity to attend a Buddhist function or to teach them how to practice. You should study more about Buddhism and take your study very seriously. If you can, find a knowledgeable priest who can be relied on to take on new converts and who is simpathetic to your stand for the Dharma. Unfortunately, many clergy can be complacent and the situation in your country may even be due to a lack of reform and engagement from the Buddhist community.
It's a tough task and a bit of a burden, but this isn't a "fight" that you started. If you endeavor to "finish" it, however, do it with compassion, equanimity, and patience. We all, however, owe a tremendous debt of gratitude to the Buddha. Whether you choose to be active against this phenomenon or to remain silent, you will still need lots of forbearance.
This essay gives a critique of Christianity, and is a good place to start if you decide to act for the Buddhadharma.
The purpose of this book is threefold. Firstly it aims to critically examine Christianity and thereby highlight the logical, philosophical and ethical problems in Christian dogma. In doing this I hope to be able to provide Buddhists with facts which they can use when Christians attempt to evangelize them. This book should make such encounters more fair, and hopefully also make it more likely that Buddhists will remain Buddhists. As it is, many Buddhists know little of their own religion and nothing about Christianity - which makes it difficult for them to answer the questions Christians ask or to rebut the claims they make.
The second aim of this book is to help any Christians who might read it to understand why some people are not, and never will be, Christians. Hopefully, this understanding will help them to develop an acceptance of and thereby genuine friendship with Buddhists, rather than relating to them only as potential converts. In order to do this, I have raised as many difficult questions as possible and not a few home truths. If it appears sometimes that I have been hard on Christianity, I hope this will not be interpreted as being motivated by malice. I was a Christian for many years and I still retain a fond regard, and even admiration, for some aspects of Christianity. For me, Jesus' teachings were an important step in my becoming a Buddhist and I think I am a better Buddhist as a result. However when Christians claim, as many do with such insistence, that their religion alone is true, then they must be prepared to answer doubts which others might express about their religion.
The third aim of this book is to awaken in Buddhists a deeper appreciation for their own religion. In some Asian countries Buddhism is thought of an out-of-date superstition while Christianity is seen as a religion which has all the answers. As these countries become more Westernized, Christianity with its "modern" image begins to look increasingly attractive. I think this book will amply demonstrate that Buddhism is able to ask questions of Christianity which it has great difficulties in answering, and at the same time to offer explanations to life's puzzles which make Christian explanations look rather puerile.
Some Buddhists may object to a book like this, believing that such a gentle and tolerant religion as Buddhism should refrain from criticizing other religions. This is certainly not what the Buddha himself taught. In the Mahaparinibbana Sutta he said that his disciples should be able to "Teach the Dhamma, declare it, establish it, expound it, analyse it, make it clear, and be able by means of the Dhamma to refute false teachings that have arisen. "Subjecting a point of view to careful scrutiny and criticism has an important part to play in helping to winnow truth from falsehood, so that we can be in a better position to choose between "the two and sixty contending sects. "Criticism of another religion only becomes inappropriate when it is based on a deliberate misrepresentation of that religion, or when it descends into an exercise in ridicule and name-calling. I hope I have avoided doing this.