I have a repeat client who needed to change my walking schedule midweek. What do I do?

He cancelled the original booking and created a new booking with the correct times/dates. I'm afraid him/I won't get paid/refunded for the first few days of the first booking before it was cancelled. I called Rover, but I had to leave a voicemail and have not heard anything back. I don't want either one of us to lose the money. Is there anyway I can reverse it or modify it? Thanks! -Marissa P.