Company Has Overpaid Me Twice Now. What Is My Obligation To Report Their Mistake?

In August of this year I received a payment from a gig job of ~$20,000 when I was only owed about $100. I called my bank to ensure it wasn’t in error on their end — it was routed to my account with my correct name and from the same account that had previously paid me correctly so from the bank’s perspective it was all good. I reached out to my job contact, and there was much back and forth by email and a couple phone calls to figure out who to even contact about this.

The company was then weird about getting the money back to them. First requesting I mail them a check. Then when I insisted I be paid for my time and the postage to mail it, they requested it to be routed to an account number. I asked several times for them to charge back the amount to the account that sent the money — as my bank had said the company should be able to do. I also requested I be compensated for the time and stress I spent trying to get their money back to them. Of course this portion of the emails was ignored.

Finally I went in-person to my bank where they were able to send the charge directly back in full to the account that issued it. This was in mid-September.

Yesterday I see that the money is back in my account. Same amount. Same account transferring it. Now 4 weeks after I returned it. I haven’t done another shift at this gig job so I shouldn’t even be receiving a payment from them this week.

Additional info: The gig job is legit and not a scam. It is acting as a patient for a local medical school and paid out by the hospital system associated with said medical school. I also suspect I am receiving the entire pay out of all the actors from that pay period as people have complained they are missing payments from August.

My questions are: What is my responsibility in reporting their error? Is my obligation any different now that this is the second time it has happened? How do I keep this from happening a potential third time?

My concerns are: Will I be potentially taxed on this ‘income’ even though it was in error and sent back? Will I again have to spend my personal time going to the bank to correct their error for zero compensation?

Location: NC

tl;dr: More money, more problems.