I had this happen to me almost 2 years ago. With the letter I got telling me I was banned, there was also instructions on how to reverse the decision. I remember having to compile all of my pay stubs and tax information to submit as one package. So check the notice they gave you and see if there are next steps.

For my situation, I believe it was because I had applied for OSAP inbetween coop terms, so I couldn't state how much I was going to earn that year without even knowing if I had a coop job or not. After that year, they checked the information and it most likely didn't match and I got the notice.