Have you had a look at the meter ?
Is it actually working?
If not they couldnt prove HOW MUCH you had ACTUALLY used over the years so there fore SHOULDNT be able to charge you.
If it is then MAYBE BEFORE you mention it some yobs may come damage it making it unreadable, and hence for you actually thinking about it and informing them but again if NO PROOF of what you have used I find it hard to believe they could put a figure on what to charge you

Just a couple of POSSIBILITIES

Steve