Increase notification re monthly subscription rate

In March my husband recieved notification from Vodacom that there would be a R10 increase in his subscription/contract payments (Sent via e-mail and sms)<br> <br> I have tried getting in contact with them since 31st March via e-mail requesting that someone get back to me to explain how this is possible when signing a contract for 2 yrs you are liable for the particular amount only over the stipulated 24months... nowhere in the contract does it state that there could and would be 'increases' or we would never have taken such a contract out in the first place!<br> <br> If someone could get back to me or my husband (Clint Johnson) asap it would be greatly appreciated.... the increase is due in May.