Billed me R279 on a R99 contract

I see that i'm charged R279 the last month for my Cell C data contract, after signing for a 24 month Contract of 24 months. I was phoned by Cell c to upgrade my contract, which will cost me roughly R120 per month. I asked specifically that the new contract starts as soon as the old one ends, so that i dont get any billing surprises. Now i phoned the call centre, which by the way gave me no joy (i will explain this later*) - and after a long conversation i realised that i was now in my 25th month, so the 'discount' no longer counts, and i was billed R279 instead of R99!! Please repay me the difference - this is just unacceptable! Please also MAKE SURE THAT THE OLD CONTRACT IS NOW CANCELLED, SO THAT I DONT HAVE 2 DATA CONTRACTS FOR THE ****LE RUNNING!<br> *The call centre:<br> first call was hung up, after making a choice<br> 2nd call i was put on a long hold<br> 3rd call, i selected afrikaans, and was put through to english, and the incorrect department, and transferred, and this lady could not even provide me with a breakdown of my invoice at first, and she cant tell me what my next months CONTRACT payment is?I need to know this,i dont need further surprises! and how can she not tell me this??