If there really is 'no discernable reason' for your utility bill (or do you mean your direct debit amount?) going up then you need to challenge it.
It will be one of the following, or a combination of more than one reason:
You've changed tariff and the unit rates have gone up.
Something's changed about your usage meaning your bills are growing (extra appliances, higher usage)
You're in debt and the supplier wants you to pay it back/catch up for winter - at this time of year you should be starting to get ahead by a month or two, because you bills will increase come October/November onwards and even if you're 2 months ahead now, in January/February, you'll likely be in debt by a similar amount.
Estimated bills meaning bills and DD amounts don't reflect what you're actually using.
Suppliers increasing the DD without justification although that's not something I've ever experienced and I think happens a lot less than people make out, because when investigated, it's usually one of the reasons above, but a lot of people don't understand the difference between the amount on a utility bill and the amount they pay by direct debit. Your bill should state an estimated annual cost based on your usage, unit rates and standing charge amount. This should be 12 x your DD amount, plus an adjustment for any credit or debt, so that's the first thing to check.