late 2015 27 " imac both thunderbolt 2 ports stopped working. what to do?

I have a late 201527" imac. I have a Akiti thunderbolt 2 external drive enclosure with a ssd drive in. I added a second drive to it and it stopped working. I assumed it was the drive. T2 drives are very hard to find, but I got a new external OWC T2 drive and it also did not work on the T2 ports, but did on the usb port. I returned it as defective but the replacement also does not work on the T2 ports. I now realise it must be the T2 ports on my imac. What can I do to try to get them to work? I am running Mojave.