Very Poor Service

My contract is coming to an end this month and I contacted Vodacom to say I wish not to renew my contract, however I want to keep my number and go onto prepaid. After giving all the info they requested, I noticed this morning that my phone tells me NO SIM, I put the sim into another phone and it says the same thing, so it is not a handset problem! This is not the first time I have had issues with Vodacom regarding this. Please reset my number to a pre-paid service!!!!!!!