Is it legal for a company to debit a card on a date that was not previously agreed upon, for an amount not previously discussed?

I have received slip shod service from a local landscaping company. I faithfully paid every month on an auto debit. The service was so horrible that I just had to cancel the annual contract. I attemted at least a dozen times to call and resolve the issues. No one ever answered the phone at their store, so I would have to have to leave work in order to speak to someone. After leaving numerous phone messages, I finally decided to sever the contract. I wrote a thorough letter explaining everything.. I even have photos of the sloppy work they had done. My understanding was they have a 25% surcharge fee to break the contract. I thought the fee was based on the remaining balance, turns out it is for the annual amount.. the amount I thought was $180, the actual amount they want is for $540. I asked them to debit $180 April 4th to end the contract, and they have come back with $540 on April 7th. I received an email to this.. What are my options as I am refusing to pay.