you can't deactivate pistons.

If you want to disable the cylinder deactivation, you're going to have to pay a specialty mechanic with a $5000+ scan tool to take apart the engine and retune the ECU. You would be paying at least $3-4k for the job to be done.

For more questions regarding cylinder deactivation- see our FAQ. https://carkiller.com/scottykilmer/qa/all-about-cylinder-deactivation/

Sell it and get something that doesn't have cylinder deactivation.

Unfortunately, I am not aware of any way to turn off the cylinder deactivation system for Mazdas.  Hondas, GM, even FCA products with cylinder deactivation have aftermarket support to turn it off, but not Mazda (to my knowledge).

Another reason I tell members to avoid Mazda engines with cylinder deactivation in the first place:  you can’t turn them off via the aftermarket.