This depends on what you were told when it was “suspended” – were you given verbal instructions? Were you given a letter? Was your card taken from you? Were you given a time frame?
Depending on the circumstances, you can contact your nearest enrolment centre to see if you can have your card reinstated or you can contact the office of the agency that suspended the card (CBP, CBSA) and ask to speak to the supervisor there (it must be the office where your card was suspended).
If the membership was revoked outright, you will have to appeal. Learn more.