Good luck with that.
I sent numerous letters over a period of 5 months all by registered post. They were all delivered and signed for but Tech Guys never had the courtesy to respond to any of them. Phone calls wee the same - "someone will ring you back" was the stock response, again, needless to say, the promised phone calls did not materialise.
The only time I received any communication from them was when I cancelled my service contract, they then got in touch fast enough but did not want to discuss my complaint or offer any apology, just wanted me to carry on with the service contract.
Needless to say they were out of luck.
There are a couple of good local computer repair shops and that is where my money will be going in the future. We also have a good local company who sell computers built to the spec you want which are reasonably priced so when I want to upgrade, it will be that company I check out first.
I wish you well with your PC repair and hope it comes back better than it went away.