2000 Mercedes Benz CLC major heating problems

In December 2013 my car heating system started to not work correctly. Sometimes the car is freezing cold, other times the heating is unbelievably hot. There is no rhyme or reason to it.
Ithe car is under warranty am do immediate,y took it to my local dealership. They kept the car for half a day. For 2-3 weeks the heating system was fine. Since then the problem has occurred every 2-3 weeks. The dealership have replaced every part and I have had two heater control panels.

The final straw was a fortnight ago, on the Thursday the car heating system was ridiculously hot, I travelled over 100miles and arrived at my destination soaking wet from the heat. It was too late to call the dealership, so I resolved to leave it to the next day. The following day I had no heat whatsoever, and ended up driving from Darlington to Chesterfield in a duvet coat. Halfway home the car started to smell of burning, and at this point the dealership arranged to meet me to retrieve the car.

Two weeks later on the heating control panel has been replaced agin, but Mercedes have not been able to find a fault.

I am now reluctant to get back into my car, for fear of it becoming a fireball as a worst car scenario, but not least the inability to control the heating system.

any suggestions.

The dealership originally offered to replace the vehicle, but were unable to find another car to match my cars specification, and are now offering a derisory trade-in price.