Scottish Power RPU issue

Hi all,
This is the first time I’ve posted in a MSE forum so apologies if this is in the wrong place.

Basically, to cut a very long story short, I have a pepayment meter with Scottish power and have since 2015. Nov 2018 I wanted to switch and phone them for my MPAN number, only to be told I couldn’t switch as I had a debt on my account. Over £2k. Investigation followed and they said I had 2 accounts, so one had all the credit and the other looked in debt. They said they’d clear the debt.

Last week we noticed credit was vanishing so I phoned to find out why. Got told £10 was being taken at a time(£100 total) to recover the debt that they had not wiped after all. Raised a complaint and a second investigation, as there was no evidence of first one. 2 days later more credit vanishes so phone back and this time get told there isn’t a debt repayment set up on the meter and he had no idea why I would have been told this.
Time frame for investigation/complaint elapses and after several calls of “we have staff off sick, it will be done by Monday” to “it’ll be done by the end of business”, one guy mentioned “looks like RPU fees” but no one would elaborate further or provide me with any updates or details so far. My husband spoke to them tonight and was immediately told that the complaint was bounced back to the advisor who raised it, who wasn’t qualified to deal with it, and who is apparently off. So it wasn’t even being worked on. He was also told an RPU fee was placed on our account in November 2018, then was taken off and refunded...then immediately after another RPU fee was placed on our account and this is what has been coming off our meter credit. £402 and change so far.
We’ve never had any notification of debt, never had a letter about the RPU or even an investigation to substantiate the claim.
And obviously, we haven’t tempered with our meter.

Basically (if you got this far thank you), my question is can we get compensation for their taking money for RPU without sending an RPU officer/engineer around to check the meter or even notifying us?