As a follow up, I called the hospital that issued the check and the representative was somehow not sure if I paid for the overpaid services with my HSA or with my regular credit card. I remember at some point in 2016 using my credit card for some services at that hospital, but I also used a large portion of my HSA for other services.
My question is thus: what would be the downside to still following what you recommend above, which is to return the check to my HSA admin and have them put it back as 2016 contributions -> get a corrected 1099-SA. Would that cause troubles with the IRS? Since I'm not sure about where the ~40$ comes from, is there a simpler way I could simply forfeit it in my tax report and have that 40$ deduced from my original return (above 1000$ for the year). I really don't care much about that 40$ being gone... Thanks!
