Terrible Service

I've had a geyser claim with standard bank last year December after having no hot water for almost a month.They changed it with Duratherm. Since then I've had endless problems with the geyser ,They've come out 3 times and I'm being told to get a hold of the supplier which I cannot not even registered plumbers can get a hold of them.only to find out standard bank stop using them now became of their inferior quality and terrible service. I have to go back and forth with them a brand new geyser now has a broken thermostat and faulty release valve,which they say I must pay after paying an excess and its not even a year. This geyser is has given me problems from day 1 and they refuse to assist please help