Internet problem on sim only contract and NO HELP

Vodacom really failed me.I called vodacom with regards to my sim not having stable internet.I told them that I am an online teacher and i need to connect to servers outside SA .I have been using this sim without problems until last Saturday.I called the call center and explained to them if they can stabilize my ping and the lady was really helpful.But the department that was supposed to help me said i should go to a store.The store said they can't help.I need help with this the speed is good but the ping is not stable.Please help