AIBU saving money on water bill question

[bigflippy]

asking on here because I can't phone unless I really have to (ill toddler)
been paying £22 a month (every month) on my water bill, they've just sent me a bill for £17 for only 10 months of the year (I know that's standard with water and council tax), so I think I might be owed some money from last year, is it worth me asking them or will they definitely have taken it into account with this years bill?

It's unitied utilities