I will not be upgrading with you again

I am not very happy with the amount that I have been charged. I was told when I upgraded that I will only be paying a certain amount per month. I specifically asked that it not be increased to more than this as I will not be able to afford it otherwise. My bill is ridiculously high per month and I hardly use it. I have been asking what this is and have had no reply I need an URGENT explanation and for my account to be rectified to only pay the agreed amount.

Thanking you,