You need to talk to a lawyer who is experienced in military law who can look at the orders to properly advise you. But, what your Recruiter probably never told you was that when you enlisted, it was for an 8 year period, which is mandatory under current federal law. Your "discharge" was not from the Army, it was a discharge from your active duty obligation, and until the 8 years are up, you would have been assigned to the Army's IRR [inactive reserves]. If you are in the IRR you can be mobilized and then kept beyond the 8 year period.

There is a process to contest the mobilization, but it's pretty complicated to do it correctly, so again, you should consult with an experienced military lawyer.

Good luck.