Mix up with contracts and bad reception

I am a customer for the past 18 years now. I always supported Mtn, but lately i get more and more bad service from Mtn. I have 3 contracts and one prepaid account with them. I wanted to upgrade my one contract account and want to port my one prepaid account to a new contract account. First of all the upgrade i wanted to do was a week special and conveniently Mtn didnt had that phone available, so it makes that contract invalid because they didnt had that phone in stock.....wow!!!! Then when i asked about my upgrade they said that my phone is on a contract which isnt because my phone is on prepaid and apparently my contract is with a 3rd party which i dont even now......wow!!!! I only dealed with Mtn so how can a 3rd party be involved?? And 3rdly the reception sucks at my aria, and yes i reported it many times but to no avail.!!!!