siemens faulty design

We bought this hob the glass was broken due to wrong design in the metal surrounding, siemens sent 3 times an engineer accepting it was a faulty part from the factory but never replaced the unit, is been six months now. Every time with a different excuse, the third engineer did not bring the replacement unit as he was not informed what to do from customer service, we think is a policy to avoid replacing costs even though the unit is faulty and under warranty. Never buy Siemens again.