I went there and explained what happened.
They were nice, though they said I really have to re-apply, but since I am on wellfare there is no need for me to wait those 3 months.
So I am now secured and will receive my new card in 2 weeks.
But to be honest, knowing that I lived here for 3 years and so in Quebec without being actually insured makes me feel how damn lucky I was not to need any medical attention during this period.
Thank you again for your kind response.