SIM SWAP Inconvenience

I was on a contract for over 5 years then i ended up getting the 8'ta unlimited contract. When this happened i decided to convert my MTN contract to prepaid and i only started to use it for data purposes and receiving calls only. 2 weeks ago i bought i new phone (Samsung Note 5) and since my new phone used a different type of sim card, i had to do a sim swap. I went into a MTN shop and requested a sim swap, i was given a new sim card and asked to call 173 to finalise the sim swap process. When i tried, the call didn't go through, i kept getting the \Outgoing calls barred"message. I called the the call centre and i was given solutions that didn't work. Eventually i was asked to dial *173# and i had to answer questions for the process to be completed. The questions that i was asked were so rigid and only directed to someone that loads airtime. I tried to explain to the call centre agent that i wouldn't remember the calls that i would've made 2 years ago"