What to do if I just had a man, who claims to be an investigator, threaten to have my license suspended due to an unpaid payday loan?

collectors improperly threaten a lot of things that they cannot legally do.  payday loans are just money owed.  they can sue you for the money but not just take your license etc.

if you are using payday loans, then your situation must be pretty bad.  a bankruptcy would give you a fresh start and stop the harassment and lawsuits and garnishments.