Useless and Ruse are a bad combination

Recently I decided to try and upgrade my cell phone package to have more minutes and data. I found out that my upgrade was due in a month and at a store they suggested I contact mtn retensions and ask to upgrade a bit earlier... in the three times I have called the call center I waited no less than half an hour on hold. Finally I got through. Mtn required that I pay upfront the subscription fees due until my next upgrade. I thought that a bit harsh but I had been having problems with my current phone and due to their billing cycle it meant 1 months subscription which I agreed to and upgraded over the phone with them promising that all was done that my new package and phone would be delivered. Three days later after receiving no documents or any phone I decided to contact them and see what was going on. After 30min+ on hold I was told the upgrade was not done due to stock availability. I spoke to person that authorised the upgrade. They acted as though they were doing me some kind of favour even though I had to pay my subscriptions up front in full until the period that I would have been able to upgrade anyway. He said that he would investigate the voice recording and revert back to me the same day. At 1620 after hearing nothing I decided to phone back. My call was answered but I was put on hold waiting to speak to this manager. At exactly 5 pm when the call center closes my call was cut off. It has left such a bad taste in my mouth since my intention was actually to increase my contract minutes and give them money. I don't know what mtn expect? Do they expect me to follow up again? With my contract so close to expiry I'm thinking it would be better to let it expire and switch. Are any other providers any better?