SUBSCRIPTION INSTALLMENT INCREASE

I would like to get some legal advice on this, as I am pretty sure Vodacom is taking a fat chance.<br> <br> Last year Nashua Mobile closed down and Vodacom had taken over all their Vodacom contracts. <br> Firstly, I signed up with Nashua Mobile and not Vodacom directly, but apparently Nashua mobile selling my contract to Vodacom was legal? Okay.<br> <br> Now this morning I received an sms advising me that as of the 1st of May 2015 my Topup subscription will increase? My contract with Nashua Mobile was valid until the 21 July 2015 and now that Vodacom has taken over 'legally', I assume my rights as a consumer is that my premium/fee/subscription fee has to remain the same for the period of 24 months? If not, then service providers can increase fees to exorbitant amounts and by being bound by a contract we as consumers will just need to pay? <br> <br> Can someone elaborate please? <br> <br> Normal working people work on budgets and I cannot see why Vodacom can't just keep the old Nashua Mobile customers on identical plans/pricing until their contracts are due for upgrade. <br> <br> <br>