Harrassment by calls and extra interest on my account due to this calls by woolies

This company decided to make my pay day the 12th of every month,the always harrass me with calls ,adding thise charges to my account cause they claim am in arrears regardless of my efforts of paying every month They always claim to escalate my querie of changing my payment datr but nothing happens.i am angry and dissappointed on this company,they are making my life a living hell