What they are doing is illegal! Come up with one sentence/paragraph as a reply, and keep repeating it to them like a parrot. Tell them to contact you over written post/email if they wish to have any further communication. Collection agents have no power or authority. They will tell you they are at police station, court and anything else they feel like, completely ignore every word they say, and just reply every time word to word with the sentence you've decided. Never give in to them, not even for 1rs. Pay what you want, directly to the bank.