is my netgear AC750 wifi range extender compatible with my T-Mobile wireless router?

I've read of a few others getting them connected. 

But try setting the extender up with the installation assistant. 

Did you set it up using the push button WPS option? 
If so, factory reset the extender  and set it up using the installation assistant.
To factory reset, push and hold the reset button for 7-15 seconds while powered on. 
Here's a video of how to use the assistant. 
https://www.youtube.com/watch?v=yJVklshxBMk