Somewhat good but admin is bad

We've been renting a property for almost a year, in September I asked for a reconciliation of the utilities bill, the agency then realized that the owner had given the incorrect municipal account so I got credited for the incorrect bill, and debited for the correct bill, in December I paid a little bit more so when January came along I knew I would have to pay a little less as we all know January is a tough month after Christmas and the holidays. To my shock and horror I got a bill that was almost double ! Upon investigating the admin lady had forgotten to debit me for the sewerage bill from April to January so there I'm sitting with a bill double my normal rent which I didn't budget for an subsequently can't pay! I don't even know what to do or if I have recourse for this. I honestly don't think it's fair cause now I'm being charged interest on an arrears account which wasn't due to my mistake! Overall the agents are amazing but the admin staff need to be more aware of their errors and how that impacts tenants. It was the Bedfordview branch