Ariston hot water unit problems from Builders express EL

Recently bought a Ariston instant hot water at Builders express East London. The unit is leaking and I've reported it to Builders Express. Manufacturers was contacted and their response that the unit is only for 3 phase electricity and I've incorrectly installed the unit and therefore I'm at fault. However the installation manual clearly shows that the 3phase unit can be connected on single phase power. I'm extremely disappointed with Builders express and how they are handling the matter. I bought unit from them and they should be resolving the matter and send someone to fix it or replace it.