MTN billing error affecting my credit record

I've had my MTN cell contract for 25 years. My monthly payment gets deducted via debit order and it goes through without a hitch. A week ago I tried to apply for a Vodacom data contract and it was declined because according to their credit check I'm one month behind on my MTN cell contract. I phoned MTN - reference *** - and in the course of 30 minutes spoke with five people; all confirmed that I was up-to-date with my account and that it was an error. However none of the staff were willing to provide me with written confirmation of this to forward to the credit bureau to fix or to contact the credit bureau themselves. I'm very soon applying for a home loan and I need someone at MTN to fix this.