Repair CAT B15 phone under warrenty

The phone keeps on saying battery over heat and then cuts out completely. I Sent it for repairs the 1st time, when i received it, it didn't want to switch on after charging the whole night.I took it back for the 2nd time.After repairs we battled to get it to switch on after charging for 1hour in the vodashop.The lady told me its only the battery that needs to be charged.After charging for 13hrs it switched on but only for 2min then it cuts out again.I charged it again 13 hrs but it doesn't want to stay on for longer than 5min, even if you keep it on the charger.Vodacom had it for almost two months for repairs and couldn't sort out the problem.I find this unexcepteble from a leading service provider.