I like to pay my bills on the knowledge that I have control of my finances, and not some utility or other company. Got stung once, so never again.
Regarding overcharging, I have had this twice in the last twelve months. The meter reader checked the usage and submitted the reading. Yet the company sent out higher over-estimated' bills (£49/£61 overcharge. Of course the usual apologies came into being, but really there was no real excuse of the actions by the utility company, other than incompetence and poor administration, and perhaps financial gain for themselves.
A neighbour of mine was recently talking about direct debit payment arrangements with her utility company. They sent her a letter/bill requesting further payments and higher monthly charges because "there had been a wrong calculation formula used". After questioning the letter, it was found that a rebate was due, she had actually overpaid the previous accounts, which I suppose came as a little bonus to her in the short term.