you should really speak with an attorney in person. Bit I-751 processing is about 7-9 months. The fact that system can't find your case, does not mean anything - they are behind in inputting the data.
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In my professional experience this cases normally take over one year. If the notice is close to expire, schedule an INFOPASS and they will stamp your passport for another year.Ask a similar question
I agree with my colleauge these cases are taking between 7-9 months for joint petitions meaning your stepdad signed too. It could take longer. . . If you get to your last month of the 1 year extension you can get another year extension stamped in your passport if the case is still pending. As your arrest may be an issue and your parents possible divorce too I would urge you to consult with an experienced immigration lawyer as soon as possible.
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