If the OP knew that the wrong fluid was used by his/her mechanic…why did he/she allow it to remain in the transmission for 20k miles?
Using the wrong fluid in any transmission–but especially a CVT–will kill it, but if the fluid had been drained and flushed a couple of times before adding the correct fluid, it is possible that the damage could have been limited. But…after 20k miles…nothing would likely save it.
Truthfully, however, I am amazed that the trans lasted that long before failing.