Why did the UMW guys only focusing on wheel alignment? If the all those test results showing within spec, but your vehicle still pulling to one side, IMHO, it's the steering rack that is faulty.

Since you'd been to so many tyre shops, had any of them ever checked the steering rack?

This is a very weird and rare case indeed

So was any qualified mechanics/technicians/foremen other than the ones from UMW able to rectify the cause of this problem? What did they recommend you to repair/replace?