Harassment for up to date payment.

This company makes many calls in a day to customers demanding payments. They have now been calling me and sending emails. The main issue is, when I ask them to share legal documents which authorizes them for making contact with me they respond rudely as if I should not be asking or I do not know my consumer rights. The payment they are harassing me with has been settled with the bank last year and I received settlement confirmation from the bank, which I shared with these people. I wonder what else should one do for them to stop this nonsense.