MTN is ****ming people data they don't put data as per the contract.

I have used MTN all my life but ever since i upgraded my contract on the 26th of October it has been my worst nightmare. I used to receive 20 GB and they took me to 30 GB option last month i only receive 10 GB and I called them till to date they haven't come back to me with an answer today they recharged my data again and yet again the only gave me 10 GB people need to be careful out there they are robing us, please can they allocate the promised data to my phone or cancel the contract urgently