7 converters in 4 years
I’m presuming they went bad as a result of driving, didn’t get stolen. Probably most common cause of early cat converter death is overly rich mixture. Gasoline heats up the converter, gets too hot, and the heat damages the converter matrix. A properly running engine passes very little raw gasoline into the converter. Is the check engine light on? Has your shop checked for diagnostic codes? Might want to ask you shop to check the engine fuel trims, tells whether the computer is having to inject more or less gas than expected based only on intake air flow. Engine not reaching normal operating temp b/c thermostat is faulty is one common cause of overly rich operation.
Catalytic convertors? Or transmission torque convertors?
If you’re talking about catalytic converters, they’re warrantied for 8 years/80,000 miles by the manufacturer.