Bad service and support

I have an Internet mobile contract with this company, which I was happy with and had no issues with at the beginning. In mid-March, I received a call from one of their agents informing me that the plan I signed up for would no longer be available, so instead, they were going to move me to another plan where I would be getting 25-30Gb of data monthly. I agreed because it was an upgrade; on the initial plan, I was getting 15GB, so I didn't mind upgrading to 25-30GB. I just got an SMS saying I only received 6GB of data. I reached out to MTN via Facebook, and that's where the agent explained that the plan I was moved to is the 6-8GB data plan. I am really not happy with the whole thing. I mean, it doesn't make sense to move from 15GB to 6 GB while I use data for everything. They told me to contact their retentions team, but the MTN call centre is a nightmare to navigate. To top it all off, the initial plan I signed up for was R99 for 15 GB, which I paid only once. After that, I was paying R198 monthly, and I was never informed why I am now paying so much. I am really not impressed with this company at all.