Stop harassing me

This company will not stop harassing a person from the 25th till month end. I have a standing arrangement to make payment on the last day of the month, which I have not skipped. They phone non-stop every single month!! I have requested an updated balance statement, on which I do not get any replies or assistance on! This is by far the worse ever debt collection company, with no one going our of their way to assist their client in any way! I would love to give them 10 stars for the worst service ever.