Bad service

Hi I paid up my account in full and I called RCS to close the account. But they did not do so and on a daily basis they send me text messages stating I owe them money. I called them many times to sort out the issue and it was confirmed it is a system glitch and I will receive a paid up letter but it's been over 2 months and it has not been resolved. And the sms always states if I don't pay the credit scores will be effected