Greetings.... Please help!

I leased a 2013 XTS base for my wife, but had the dealer install heated seats. The obviously sub the job out. Now, the seat belt alert for the passenger seat dings on a continuous basis, unless we keep the belt buckled (when nobody is
sitting in it)! We took it back to the dealer, which tinkered with it for a day, and ended up saying... either disconnect
the heated seats, or keep the seat belt connected!

Does anybody know what may be causing the issue, and know of a fix for it! We live in the north...Disconnecting the

heater isn't an option!