MTN overcharging

One of my cellphone contracts ***) was due for an upgrade, I went to MTN Bonaero Park on 23 January 2020 and upgraded. The contract I signed was R439.00 per month for 36 months. Today I received my first invoice and they are charging me R721.20 per month. I have not even contacted MTN to rectify this, as I know from previous experience that it is very frustrating, thus I decided to just review them that can be made aware of the fact that their service is not satisfactory, and that they would rectify it. MTN deserves no stars at all, but unfortunately I have to give them one star.