contract changed without my knowing

I Was due for an upgrade when I received a call during my lunch break advising me that it is easier and more convenient to do the upgrade over the phone. I did accept and offer but the next day my phone did not work(no network) I went to the store and did a sim swap. The following problem is that I cannot call any other network than Telkom. On my previous contract I could call other networks as well. This is a huge problem for me because I don't have too many family or friends on Telkom network. I feel its a waist to have 3000 minutes to Telkom only. The minute is accumulating while I must buy extra airtme to call family and friends. I possible please revert my contract to the previous one. Thank you.