Standard Bank Blue bean credit card

I was handed by Standard over to Brooks and Luyt attorneys for owing on the blue been credit card account. I made an arrangement with them and paid every month. I managed to settle the account and received a letter from Standard Bank conforming that account was settled. I am now being harassed by Brooks and Luyt call center people. They keep on calling after i had forwarded the letter from Standard bank. I have so many times asked them to sort this out with Standard Bank , but the have not. I am really annoyed about this.