How long is too long to wait for adequate service?

There has been times where I paid more than once for my cell phone contract. This didn't occur on a monthly basis so I thought that it could be due to data usage or too many calls I made. A month ago I went to the main branch in Somerset West and find out if it was the case. We found out that I've been paying for another client's contract. MTN made the mistake to use the same bank account number (mine) for two people. Just a mistake, but more than R2000 later I asked if I could get my money back which is rightfully mine. Timothy, at the Somerset Mall branch promised me that it would take 2 days. That was on the 19th of September. After that I have gone to the shop more than 5 times to ask for assistance.. an Isaac \helped"but I still haven't heard back. After going to Waterstone Village's branch 10 days ago Vivian Wingyou promised feedback within 2 days"