Want to pay account not received after indicating will only charge partial

We have never received over a twelve month period a bill for rates and taxes. Then when we moved out and wanted to get our deposit back, they admitted they only now received the bill from the owner, they made a mistake and will only require us to pay the last two months, as it was their mistake. Then they backtracked and said we have to pay the full 12 months of rates and taxes to the value of R25000