Paid up Letter Hustle.

I have an account with Truworths which the account was handed over to Nimble Group for payment and the account was fully paid but now Nimble Group is not making my life easier as I have been sending proof of payment so I can get the paid letter but this company they don't respond to their emails as well as their WhatsApp number,

The only communicate they do is to send me sms where they don't do communication, this has been a hell of experience since this is affecting my credit score with the account that it's been paid, the only thing I want from this Nimble Group it's a paid up letter so my name can be cleared