**** debt collecting company

I'm sure this is a **** debt collecting company. I paid my outstanding account on the 29th August, was promised a paid up letter within working 21 days and to this day, I haven't got it. They responded once on email to say they are waiting for the letter from Cell C. I sent them another email today asking for it again and the email bounce back saying the mail box is full. My advice - Don't pay them!