Guest,
Generally creditors report your account to CRA. It seems your bank did not inform Chexsystem about your account, which might be the reason your Chexsystem was clear one year ago.
However, as you have mentioned that you have no idea of these overdraft fees, ask the collectors to validate the debt first. Third party debt collectors must provide valid proof of the debt that they are collecting. It will help you understand how much legitimate it is.
So speak to them and get their address. Then send DV letter, make it certified.
Also consult a lawyer to confirm the statute of limitation of the said debt. SOL in NJ is 6 yrs. Still it would be better if you can verify it from a local lawyer and be sure when does the clock start for this specific case.
Hope this helps. Please keep us informing on what is going on.