That is very odd. Unpairall should have worked, but perhaps there's something wrong with the antenna or maybe the firmware chip? I'd need to look at it in person to be sure.
As for what kind of repair it is, that depends on the issue which I simply can only speculate on right now as I don't have it in front of me. As far as the actual cost, there are two possibilities: Either you're within the warranty period (1 year from purchase, typically) and the device is still covered (no major physical or liquid damage) then the repair will be carried out under the warranty at no additional cost to you.
If not, the service center will assess a fee for repair and offer you a quotation between 105-135$USD depending on the scope of the process (basically, repair components or replace unit in whole)
Edit: Beyond the warranty period, devices are not eligible for RMA repair.
Thank you,
-Jack S