So I've gotten a pretty horrendous water bill that I'm not sure what to do about. I've ignored it for a bit to figure out some stuff I'll explain in a minute. If you think tl;dr, go to the bottom of this post.
To sum it up, for the last 18 months we've been paying what works out at roughly £40 a month to Anglian Water for the privilege of tap water and flushing excrement away. As I'm sure you all know, these amounts are always an 'estimate' and luckily this has left us ~£250 in credit. I thought that was excellent news, thankyou very much Anglian Water for being a piggy bank. NO.

Next bill I get after the meter reading guy comes around (I think this was in January!), just shy of £600 for the period Jan-July. Apparently our water meter reading thing had almost tripled. Leaving us with an 'estimate' of £103 per month. For some reason this wasn't queried when the reading was done, and we were in the dark about it as I don't go and read my meter all the pissing time (it's in a 2 foot hole under our wheelie bins). So 6 months pass by, with no change in our circumstances i.e. we didn't suddenly start showering 43543 times a day or have anyone extra move in, and for a total of around 10 weeks I was actually home alone, ergo less water consumption! So we were left with this 600 quid bill, luckily the 250 we're in credit by has reduced it somewhat.
Phone calls have been made to these guys and they said we have to do flow and leak tests, etc. etc. Tests were done, everything is fine. The meter seems to be working fine, although I am no meter genius. The bloody person on the phone even said "Yeah it's really weird how it's just jumped up like that, something doesn't seem right."
So to sum up:
18 months @ £40 -> 6 months @ £103
We haven't done anything different, all is working as it should, Anglian Water say it's weird but still say we have to pay.
Any advice?