Mediocre Service

For the past two weeks i have been liaising with Momentum to have a tax issue fixed. Momentum dupicated an IRP5 sent to SARS to make it look like i earned money that i didn't earn and as a result i am being hounded by SARS about tax money that i don't owe. The guy i am liaising with at the Call Centre (Alex) has been making empty promises to me for the past two weeks. He always promises to have the issue fixed by end of day and promises to call me back. All of which he never does. How am i suppose to resolve this issue with SARS if Momentum wont fix their stuff up?