pedal crank moves and tries to slip off the axle
My guess is that by the time the first bottom bracket (crank axle) was replaced the left side pedal arm was also damaged. When you installed the damaged crank arm to the new axle it worked for awhile. You are now at the point that you have a worn arm and a worn crank axle. Replacement of just one of the components will result the premature failure of the other. You need a new bottom bracket and crankset. As this is an expensive repair it may be worth looking for a used assembly that is in good shape. The crank arm bolt should be tightened to about 30-35 ftlbs of torque. This takes quite a bit of effort with the average 6 inch long allen wrench.