Ouch... hopefully the guitar's got a whammy bar and so then the trem was just pulled up rather than detached from the body. If it's a hardtail (that is, the bridge is physically attached to the body; no springs in the back) then it was definitely a bad thing that happened.

Part of the problem is switching to 12 gauge strings. Cheaper guitars aren't generally built strong enough to withstand the added stress. Actually, you really shouldn't be jumping around gauges too much... maybe 10 or 11 if the guitar shipped with 9s.