Trying to get service from a service provider

I had a billing dispute mid march. The lady in store said that they had numerous other clients with the same problem, top up requests has not been honoured. So, after more than one visit to the branch (which always seem to be offline) and a Face Book complaint they promised a credit. Declined credit after the fact.. never notified me. They also say they have tried to reach me, which I strongly doubt, as I have personally made various visits to two branches, countless phonecalls and emails... and the original problem has not yet been solved, not to mention the credit owed to me... The one Manager actualy said that it appears as if the branch is covering up the fact that they are responsible. I have been a loyal client for more than twelve years, but I suppose it is time to move on..