Trying to charge a user too much

[#1]

I saw my neighbour from before we moved yesterday who is also a Plusnet user. A while back I pointed out to him that our exchange had become Market 2 and he moved to Value at the Market 2 price. On his last bill the price jumped to £12.99 (the Market 1 price). He raised a ticket asking why and was told that the exchange was NOT Market 2 but Market 1. He challenged this and eventually there was a response from someone who knew what they were doing and has reset the price accordingly (although at that time he hadn't been given a credit for the overcharge).
I find this worrying on two accounts: firstly that the system had him down as the wrong Market and bumped the price after 3 months, secondly the initial responses stating that he was on Market 1 when SamKnoes and Usertools exchange checker said it was Market 2 - just what list was the person who made the initial response using?

[#2]

Hi John,
Our staff are encouraged to use our own internal tools prior to those of third parties.
The agent has correctly looked in one of our systems which shows the service to be (incorrectly) in a Market 1 area. The person who followed up, has dug a little deeper and it appears that the information held on our system is incorrect.  I suspect that this may be as a result of it not updating on this account after the last Ofcom market consultation.
Either way, all appears to be in order now.

[#3]

Thanks,
Has he now had the credit/refund?
Has the internal system now been updated so something similar doesn't happen to other users?

[#4]

I can't really comment on the account other than to say that it's in hand.
I'll raise a task to have a look at other customers on that exchange to ensure that the correct information is present.