Send it back
Choke tube should need replacing when your barrel does, which is to say, never, unless perhaps you're Tom Knapp.
And most companies will tell you, their turkey chokes are absolutely not for steel shot, and especially massive pellets like T shot. If you did want to fire steel through them you'd want to shoot something like 3, 4, or 5 shot.
I'm dealing with finding a choke tube company that makes a super tight choke I can shoot steel through right now, I ran a Terror chokes (now gone for all intents and purposes) .655 in my 12 gauge, x-full waterfowl chokes are usually .690'ish territory, sometimes you find them to .675. That is to say, I was running an extremely tight choke. I spoke with the President of Terror chokes at the time, he said, shoot 3 shot or smaller in that .655 and you should be fine running steel. Loved it. Now run a citori 20 gauge and think I've found someone who will play ball on providing a super tight choke for steel shot.
So, depending upon the materials they use, yes, you could have ruined your choke shooting improper shot through it. However, like I noted, I would send it back with a note, "I've been using this choke for x years, it has developed what appear to be channels running through it, it isn't performing as it originally did, please replace with a product that works."
Or something of that nature
It's probably your fault for neglecting the true use and manufactures intent of the tube, but as they say, "anything not overkill, is underkill," and they should have used better steel/treatment.
You may want to check the threads and end of your barrel as well, because if that choke expanded, your barrel went with it, and you may need a different tube now.