Vodacom is in breach of contract and lying to me about the details

On Sunday 3 September I signed for a new contract to be loaded onto my existing line for my mother. All paper work done and signed a contract for X value. The porting of the line was requested from MTN and approved. A SIM card to the value of R1 was sold to us with the instruction that when the MTN line stops working the new Vodafone sim needs to be inserted and then my mom needs to make her way to shop to collect the actual handset as per the contract signed. On Tuesday night the MTN line stopped working and my mom went to Vodacom on Wednesday morning for assistance in swopping the sim which was done but still in the old handset. Due to time constraints it was agreed that she will return on Friday (today). Today she she returned to collect the handset and for Vodacom to assist her with data transfer the breach in contract occured. I was informed that due to the change in specials which occurred yesterday I now have to Y rand more per month. My mom had to take the phone as signed for on the higher price. I spoke to Willie the consultant and the assistant manager Sanchan. Sanchan expressed his view that my mom was. It in the shop on Wednesday but on Thursday hence he will not approve the old price which I signed for last week Sunday. In my view this is breach of contract and me as the consumer should not be held liable for the additional cost. I am agriefed with the fact that a manager was not willing to assist and claims laid that the communication gap is between me and my mom on the day she was physically at the shop.