there is more to the Statute of Limitation than the time the debt made originally; there is also the fact the time period may have been expanded by different factors. If I received a call, my gut reaction would be to tell you to ignore it, but you would have to talk to a local attorney to get a more precise answer relating to your situation.
The most important issue you may have is that payday lenders in Maryland rarely comply with the payday filing requirements. They may not have a legitimate claim to begin with.
That said, the Statute of Limitations does expire in three years, but that is a general rule. The 3yr limit can be extended (tolled) if you make any payment or acknowledgement of debt. When was the last time you, or anyone representing you, spoke with the payday lender/collector?