Question regarding a tax return

[LMAO]

Received a lovely letter of reassessment from Revenue Canada today. The letter states that my 2012 tax return was off my exactly $10. Not such a big deal until you consider the fact they calculated interest on that $10 from then to now.. I had my taxes done by a professional at an Easy Tax location as well. The letter says I owe just over $800 to Revenue Canada. I'd like some tips from you. Has something like this every happened to you or anyone you know? What should I do in this scenario?! Thanks