Imagine a company with a direct debit set up with a bank account takes £1.50 out of the your account which puts you £1.50 overdrawn on an account without an overdraft.
You then immediately level the account to £0 on realising the fault and the bank charges you £28 putting you £28 overdrawn again after levelling this cost you phone them and they tell you they will charge a further £20 next month. Presumably the cycle will then continue unless you put extra money across so it doesn't go in the minus.
You then send them a letter telling this you cannot justify a £28 charge for a £1.50 infraction which was immediately rectified. You also tell them it was there action which put the account overdrawn again which triggered the next charge. You tell them it's unjustified and to at least drop the future £20 charge as a compromise. If a comprimise isn't even met you will take them to Ombudsman to settle the dispute.
The bank then tells you they see the charges as fair and they still stand.