Being overcharged not updating to new contract

In April I changed to the new all inclusive SKyPakcage of R1899. Trusting MTN as I have been a loyal customer for years I did not check my bills as it should now be stable at R1899. Yesterday I checked my bills and I have been charged R3800 up to R4200 per month. They only updated me to Sky in September<br> <br> I want to warn everyone to double check their billing from MTN as this is a huge mistake and now i have to wait for 5 days for them to check on this.<br> <br> I am not sure how they are going to resolve this and repay me for the interest I have lost because of this.