Disappointed customer.

Good day.

I want to lodge a complaint. I owned a LG microwave, the biggest one, for many many years without any problems. It eventually broke, due to age, which I can totally understand. My problem now is this... I bought a new one which is also very nice but started giving me problems a few months in, since I bought it. I took it back to Hirches where I bought it, they booked it in for a check up and phoned me 4 days later and told me to come and pick it up. When I got here they said that nothing is wrong with the microwave. Up untill today it still switches on by itself, the time is constantly 6 min ahead and it sets the defrost function on by itself. How is this even possible? But "apparently" there's nothing wrong with it. Answers please LG...