Extra Energy - A Warning

Just a warning about this company:

I used Extra Energy in 2014/2015, there didn't appear to be any issues with the service, and I cancelled and paid the final bill when I moved out of the property in September 2015.

Fast-forward to spring 2016, and they email me telling me I owe them £7. This was the first I'd heard from them in over six months. After many emails and phone calls, and despite the fact I could demonstrate to them how I didn't owe them £7, I decided just to pay it as I was going through a mortgage application and didn't want any 'issues.'

However I still kept receiving emails and texts stating I owed them various small amounts: £2.71, £1.86, £5.24, etc. Eventually I managed to get an Extra Energy manager to confirm in writing, via email, that I owed them nothing and I should ignore any future correspondence from them...

Well... today, almost two years since I thought this issue was resolved, I receive an email from Extra Energy (with accompanying text requesting I call them) stating I owe them £26.57. Having logged back into their online system it states I owe them £1.26. :mad:

The people I've dealt with in this company seem okay, but whatever computer billing system they're using is clearly utter pants. And evidently they've not elected to fix whatever issues they have, even two years down the line. The hours and hours I've spent trying to resolve their issues for them since my contract ended was not in any way worth their competitively-priced service. Based on my experience I'd suggest avoiding this company.

Any similar experiences?