They've got a number auto-generated into your line somewhere. This happened once but three times is incompetence in the payroll department. Of all the things you lay multiple sets of eyes on, it's payroll.

Unfortunately, there's not much to do here, other than continuing to remind them they keep screwing up, and it's a pain in your ass. There's no regulation that I'm aware of that helps out. Only underpaid is an issue, but they've got time baked into those regulations to fix errors as well, blah!