Is there anything between a T15 and a T20 torx that I can use. I have tried three sets and none of them worked. I have even tried using allen wrenches both metric and sae. Please help
No. There's no bit between T15 and T20.
My suggestion back to you is, maybe it's not a Torx bit you need. It might be something other than a Torx (there are a plethora of different bits). Secondarily, you may have stripped the head out. (Note: A picture in your question of the screw you are trying to remove would have been helpful here.)