Still no response

On the 17th of February I contacted the call centre to verify that my account had been closed last year, as it still reflects as an open account on my credit report and is affecting my rating negatively. The friendly call centre agent confirmed that it had been closed. I requested a letter stating this and he said that it will be sent before close of business, or early the next day. 10 days have passed and I still haven't received this letter. Can someone please escalate this so that I can correct the errors on my report so that I do not get rejected when applying for a bond!