We rarely see any posts about the retractable towbar, let alone positive responses. Either they're generally fairly reliable, or there weren't many fitted.
I can't recommend anyone specifically in your area but would suggest trying either a Ford specialist or even an auto-electrician next.
The towbar system can't be that complex. Essentially it'll just be a few sensors and a motor. I would have thought Ford's diagnostic system could at least provide a fault code as to which of those might be causing the problem. If not, will just have to methodically go through plugs, wiring, sensors etc, make sure everything is clean and tight until the cause can be found.
If you don't use the towbar, you could pull the fuse for it to stop the beeping, as long as the fuse doesn't cover any other circuits.