Timing belt continues to skip..a.nd seems to jump teeth tho I've carefully put it on today 3 times .Then the belt has loosened?

 

Year of car and engine type, V6 or 4 cylinder?

How many pulley teeth are being "jumped," as in 1, 2, etc. and is this consistent?

The belt is not jumping a tooth. Assume the issue is the when the slack is removed from the belt, the cam pulley is rotating but the crank pulley does not. The result is the cam/crank pulley timing is now off.

You might rotate the cam pulley CCW the number of teeth being "jumped" then install the belt. When the belt slack is then removed, the pulley will rotate CW but the crank pulley stays still. The result can be perfect alignment.

With pulley tensioner loose and belt installed, rotate the crank CW to put tension on the belt. When still rotating tighten the tensioner bolt. You need to tighten the tensioner bolt went the crank is being rotated CW.

Don't rotate the crank CCW doing the tensioner tightening procedure.

As usual when finished, rotate the crank 2 times CW to confirm the alignment is still correct.