Good morning Jurgenjay I have studied your posts and it's obvious that you have been treated terribly, unfortunately this seems to happen quite frequently with the shortage of good tradesmen and the ease that someone can set up as a so called installer , the sign of a good tradesmen is what he does when something does go wrong in this case it seems very little.
Now what are your options ? You could go down the small claims court route but it will be a lengthy drawn out process which alot of people don't have the stomache for and end up giving up.
You could complain to trading standards no reputable company want to be investigated by them as it will blacken their name,
The company you employed has a duty of care to carry out the work as agreed the job was either carried out by a subcontractor or now ex employee but the responsibility lies with the owner of that company.
Was a detailed estimate or quote provided stating what work was to be carried out ?
What is the relationship like between yourself and the company ? has it broken down and you are being ignored ?
The bottom line is do want this company in your property? you've had a bad experience and at best the work will be patched up and cause issues for you at a later date , legally you need to give him the opportunity to correct the work but it very rarely ends well as you have no confidence in him and he probably sees you as a irritation.
The best outcome would probably be to employ a reputable company to correct the poor installation and try to recover a percentage of the cost from the original company, it really comes down to whether you have the time and are willing to perdue this individual relentlessly it will take a long time with no guarantee of a good outcome. Regards kop