Remedies against marriage registered with fake certificate

My cousin Pooja was in love with a boy. That boy take her to register officer with his family and did Register marriage by submitting a fake marriage invitation ( to prove marriage has already happened in a wedding Hall). But no marriage has happened like that at all. But the marriage is registered now. But they didn't live together even for a single day. Now my cousin wants to come out from this problem. But that boy threatening with the marriage certificate. What should we do now? Shall we proceed for a cheating case or go for a divorce case?. If cheating case means how long it will take to get closed. Religion - Hindu.