MTN is responsible !!!

I was contacted by an agent who sold me an MTN package for a new cellphone contract. Once the contract started the package was nothing like what I discussed with the call center agent. I have been to the MTN store and spoken to people over the phone and sent emails, but I have not been properly assisted at all. MTN tells me that I have to deal with the call Centre that sold me the package. But what I don't understand is that MTN sold me the package and on my bill it says MTN and my number is an MTN number, but yet MTN cannot help me, I have to go back to someone else. NO.......MTN must sort this out. Their contract, their bill and their number...MTN takes your money but does not assist you...