You might have a variety of issues. I have never heard of a case of an auto lease being reported as stolen. The UCC (the statute applicable to your case) provides a structure for how a secured creditor like BMW can re-possess the automobile. You do not seem to possess the requisite intent to permanently deprive BMW of its automobile, seeing as you know it is a lease and intend to give it back at the end of the term.
I am concerned that the debt collector threatened criminal action against you within a sufficient basis. That may violate the Fair Debt Collection Practices Act. I would speak to an attorney if you are continuously threatened like that.
Christopher R. Minelli
Minelli Law Offices, LLC
NOTE: This answer is not intended to be legal advice and should not be construed in that way. This answer does not create an attorney-client relationship and no such relationship may be created absent a signed retainer agreement. The author is licensed in Illinois only, and his answer is for educational purposes alone.