You can injure tendons in the groin, and when that happens, it can last a LONG TIME.
It might not be piriformis at all.

I had a fall and strained some ligaments there, and had IFc electrical stim and ultrasound and the pain went away. I was unable to return to the same flexibility however after 3 months of PT. I think you may have a groin injury and not piriformis at all.

The lidoderms need to be applied to the lower sacral area on your back for best results. That is where I used mine. This intercepts the nerves before they enter the spine.

I will say a groin strain takes forever to heal up. When mine occurred I couldn't even roll over in bed !
Of all pain relievers, aspirin worked best 3 times a day. I used Alka Seltzer original formula because the aspirin in it is soluble and doesn't affect the stomach so much. This simple thing gave me a bit a relief until I could get home (we were on vacation in the boonies) to PT.

For spasms I'd look into magnesium to relax those muscles.
Topical works very well in lotion form. CVS has an Epsom lotion, which they are foolishly discontinuing, but some stores still have it on the shelves. Another topical is called Epsom-It. It is made for feet but it will work anywhere you need it like the CVS one.

Oral magnesium will work too, but avoid mixtures or any that say OXIDE on the label (oxide is not absorbed from the GI tract). Don't do HEAT... but try some ice once or twice a day. Heat stimulates nerves and injuries. Try the ice in the groin area, or on your lower back. When I had the IFc (inferential current --which is different from TENS) the therapist put an ice pack over the electrodes to ramp up the current and suppress pain . It worked really well for the acute stages of pain that were incapacitating. Since all your interventions for piriformis are FAILING, I'd look at the groin area instead. That may be where the pain generator really is.
Just my opinion.