Problem with Three continuing to send bill after contract ended

lynemacgregor

My daughter, Helen, who is disabled, took out a two year contract  with Three on 15 May 2021, at their Inverness shop. She got a Nokia 1.3 mobile phone. The phone broke down in May, and she took it back to the shop who gave her the address of a Nokia repairer in Dundee. She sent it there and it never got to the repairer, as the firm did not exist. After many email to Three, letters and visits to Royal Mail sorting offices, we got an apology from Three, compensation of £20, (email from Three 17 June), and Three agreed to terminate the contract forthwith with no early closure penalty. We were told that if we received any more bills just to ignore them. My daughter has been getting bills ever since. Then she received a letter from Three, in  Sep undated, to confirm that her contract had indeed ended on 20th June, and that she was in credit of £14.55, which would be refunded within 14 days. Then on Sat,  5th Nov, she received a letter from CARS, a debt collecting company, acting for Three, asking for  £30.92. I have informed them that Helen is not in debt to Three and have not paid them. 
My wife and myself are well into our 80s, and find this all extremely stressful, and your advice would be greatly appreciated. Our daughter cannot deal with this herself.
Robert McKenzie