Re: Regulator??
If it's Direct Debit, complain to BACS.
I went to remortgage a few years ago and as soon as the existing mortgage provider knew I was moving they stopped collecting my direct debits and reporting me to Experian. I complained to BACS and explained what had happened - and significantly, when it had happened - and my mortgage vendor very quickly decided to change my credit file to say I'd made my three payments on time.
I complained again a few years later over council tax direct debits going AWOL - again, their cockup (this time they were collecting them, but not crediting them against our account). I was later told that BACS threatened them with losing the ability to take direct debits if they didn't sort it out...