Context
I can provide more context to the story (question), but I also want to keep it short. I have been paying my accountant for helping with my corporate taxes for the last 4 years in Toronto. I was paying for the corporate taxes about 30-40% higher above the average for the same work my colleagues are paying. In return, this firm has offered to file my personal taxes for free. Which did successfully happen three times previously. It was a gentlemen's agreement and I have no proof of this agreement in writing. At the same time, he naturally never invoiced me for this work either.
Question
This accountant has suddenly sent me an email saying I never paid for filing my personal taxes with him for the last 4 years. The invoice is asking to pay $350-600 + HST per filing. For myself + my wife. Our taxes were really simple with simple T4 forms, nothing fancy. In fact, I used to use TurboTax and it took me 30-50 minutes to file on my own. So the invoice total is about $1600+ for four previous years of personal taxes for myself and my wife. Can I legally ignore these invoices? It does not make any sense that he sends me invoices for work done 4 years ago. Would really appreciate any advice!