Paying customs from the post office

So my relative has sent a gift from UK. It consists of few baby clothes, toys and some colour pens. I recieved a call from the Indian post office saying that I have to pay customs of approx 6k. They shared a reciept of the same too, it had signatures of few people. Is it really genuine?? The gifts are worth 2k. And I'm not willing to pay 6k. Is it an offense. Or is it a scam. Please help.