Desperate Plea for help

I had a simple bumper repair done over a year back. I've been back 3 times for them to fix the problem, but my bumper is still not done correctly. I'm afraid that this might influence the value of my car, as it still fairly new (a 2022 model still under warranty). I took the issue to management on 26th Sep.'23, after the service staff spinned stories and still gave my car back with it not being 100% right. I received a swift reply from Bradley, and a personal visit. This was accompanied by a sincere apology and a SURE promise that they will get it done right this time, and even arrange a courtesy car. Tomorrow it will be 6 weeks later, and still it has not been done. Bradley acknowledged that he was not made aware of my come-backs and the problem that remained unchecked. They guy that helped me with the last complained, has apparently left their employ under a cloud. Now I'm left searching the internet for contact details of the boss, writing even more stern emails and resorting to basically threatening to inform both Haval and Momentum, that maybe this company should not be on there panel of preferred service providers anymore. I'm desperate and don't know what else to do. Bradley also promised that the workmanship guarantee won't be affected by their delay. I told him I would like a new guarantee issued to me once this repair is finally done, as I've honestly lost faith in this company to keep their word. If anyone here can tell me what to do, I'd appreciate the advise.