Vodacom Contract Issue

I took out a contract with 2 phones and a free sim card, the sim card received R75 airtime free for the duration of the main contract.. Now the contract has lapsed and suddenly I am charged. Tried to phone Vodacom on Friday just to be told sorry you can only cancel in May as it has reverted to a month to month contract but you are tied in for 3 month. I can cancel now but will be charged a penalty fee. How do I get this contract cancelled without having to pay penalties. Vodacom can even check that this number is not being used. How can you just lock someone in for a 3 month period without communicating this. Number in question ***. Not happy at all with this will be cancelling all my contracts as they lapse. Have been a customer with Vodacom for over 20years and then this!!!