Extra charges

I have taken a contract with this service provider at an agreed amount of R129 pm x 24 , so far on more than one occasion i have been billed a much higher amount infact double the agreed amount , i know this cant be becuase i use the card for the airtime only and it is put away for the month . I do not buy bundles and it is meant to be a capped or top up contract, i have queried it previously and was told its sorted out . I have yet to receive a refund and my patience is wearing thin, unlike many others i check my statements , i also am aware that there are many people with this issue and i think its about time we let it go viral so we can help others being ****** of there money. Please help