Price increase on contract from 1 May 2015

I started 3 x TOP UP 1GB subscriptions @ R69.00 a MONTH for 24 MONTHS on the 24th December 2014. <br> <br> Yesterday I received 3 x e-mails from Vodacom saying that asof 1 May 2015 each contract will increase from R69 to R75 per month.<br> <br> This in UNACCEPTABLE!!!!! I signed a contract for R69.00 per month for 24 months... the reason I chose this contract was that I would know for a fact that I would be charged ONLY R69 a month for 24 months...<br> <br> I need someone to sort this out, I am sure that I am not the only unhappy customer regarding this!!!