hmmmm...metal between the internal antenna and the towers....no wonder you have signal issues
Putting a phone with an internal antenna into a case that is made of metal is a big no-no if you don't want a considerable amount of signal loss.
It's too bad that you found the case of your dreams only to find it kills the sig. I wish I could suggest a solution, but the only one that will allow the phone to work as it should is to ditch the case!
Good luck!