There are several models of the Wellworth.
Without seeing a picture of yours, it would be hard to comment.
The older ones with the 2" flush valve were never very good.
They are supposed to be coming out with a large canister flush valve that works better.
I still don't care for the trapway on those.
With new 1.6 gallon toilets, it's rare that it overflows with a plug, unless it's flushed twice.
If plunging doesn't clear it, you may want to invest in a "closet auger"
Then you can do your own repairs.
The trapway on the Drake is a better design, but nothing is absolute "no clog".
All things are possible.
Link about the chain tangling on the new canister flush valve