There are many things going on with you...your spinal issues and the drugs you take are major factors.

Do you still take the benzos?
I'd look at those first. Long term benzo use, results in tolerance and when that happens and you need a dose increase, cramping may be a signal.

When mag is low there are other muscles besides the calves
which cramp. Back, hamstrings, ribs, neck, toes. (I've had all of these at one time or other.)

The calves only?

Magnesium only works in those depleted. It will not work if
you have other issues (erratic benzo consumption), stressing the muscles with shoe changes, foot issues, low potassium,
pinched nerves in spine, low iron (as Shelley points out),
smoking, low O2 from apnea, dehydration/heat intolerance, elevated thyroid, many other things too.

I've posted before...and will say this again, Liza...you are a very complex medical case. I don't think there is a simple answer for you. I have links about magnesium on the Vitamin forum.