per Toyota's Repair manual.......
If you can't get the tensioner to move, then you might need to replace the assembly. Just like you said, cut the belt, remove and replace the assembly, and reinstall the new belt.
.....which is what you've done.
If you can't get the tensioner to move, then you might need to replace the assembly. Just like you said, cut the belt, remove and replace the assembly, and reinstall the new belt.