You will need to contact your GAP insurance company to find out how much, if anything, they will pay on a GAP claim for your stolen vehicle. If your insurance company is denying your comprehensive claim on the stolen vehicle then the GAP insurance company may also deny your claim.
Typically GAP insurance pays the difference between what your physical damage coverage paid and the outstanding lease or loan balance. If your primary insurance provider is not paying actual cash value for the stolen vehicle on your physical damage claim then it is unlikely that GAP insurance would pay out either.