MTN and Mondo service is horrible!!!

I have had the most terrible experience with Mondo and MTN with my contract upgrade. First they added my upgrade to my account and dod not remove the previous contract bundle (which charged me R1800) and then after (I stopped counting) numerous phone calls and emails wirh both companies they proceeded to hold me liable for all the fees. Now MTN is saying Mondo needs to sort things out and Mondo is saying MTN must sort things out. I am tired of their bullsh#t. I refuse to pay my account until someone sorts this out. It has been almost 4 months of trouble.