I suspect your specific issue is that the GM "Body Control Module" has lost (or never had) the unique RFID for the offending sensor. Since they all work on 315MHz, each sensor must scream out its unique coded Radio Frequency ID so the BCM knows which tire is low, and not get confused when passing another Malibu (or Tahoe, or other GM vehicle that shares the same system) and report your neighbor's tire pressures rather than your own.
In your case, I'll bet the sensor is communicating just fine, but the BCM refuses to listen. Perhaps the difference is in the word "communication" -- while I have one definition, my girlfriend may have quite another...
Unfortunately, I think yours requires some specialized tooling to trigger the "learn" process which binds the sensor RFIDs to your personal BCM. Some vehices use a powerful donut shaped magnet placed around the valve stems to trigger this process (I own that tool), but if I recall that's for Chrysler and not for GM. My expensive SnapOn scan tool can't even do it, along with other GM woes like radio replacement, keyless entry, HVAC controls, or instrument cluster repairs. The imperial BCM is quite the dictator, and the complexity makes it very difficult/expensive to perform certain repairs by independent shops.
Now, if this worked before you took your vehicle in to get "fixed", I feel the repair shop owes you a BCM TPMS synchronization. On the other hand, I've seen major tire shops that disclaim this in their receipt fine print, because again some of that tooling (handheld computer thingy) is eye-watering expensive. And the sensors themselves can easily get broken if you aren't careful breakihg the tire off the rim.