I had the "closed" issue for a flight I cancelled in October when I tried to use my ecredit in November, BUT everything on my end had been booked through Delta direct. However, I was able to get it resolved via text. They could see I already checked in for the flight and for some reason when I cancelled there was a glitch that left me checked in, so the ecredit never got to a usable state - chat was able to resolve it for me. Based on the timing, I do not think this is your issue, but perhaps there was still some other technical issue. I would suggest trying to contact again and do not bring up Chase, just tell them you have an ecredit that you are trying to use but it says closed but that you have not used it nor are you past the expiration date.