unreachable con company

I had a gold cheque account with them and i got a premier account and they did not close the gold account and it accumulated charges and was handed over to their legal division and i made arrangements and eventually paid it off, now the account owing zero just got monthly interest charged to it and i cannot even close it as i cannot get hold of them, i have sent countless emails to no response or resolution.

Its affecting my credit record badly as i can get them to close it or at least provide a paid up letter.