Garage Band inputs and multi tracks

I’m running Garageband on a 2017 iMac with Mojave. I’ve got 2 mics running through a small 2 channel mixer/usb audio interface. I’m trying to simply record 2 mics, on 2 separate tracks, at the same time.

So, I set up 2 tracks. Each track is assigned an input. Track 1 is on input 1, and track 2 is on input 2. On the mixer/usb audio interface I have a mic plugged into input 1 and another mic plugged into input 2. The problem is this. There is no separation in the tracks regardless of input settings. Both mics are registered equally on both tracks as if the input is set to “1+2” for each track. I tried unplugging the mic that was assigned to track 1 which means GarageBand shouldn’t be registering anything on that track any longer. But it was... the sound from mic input 2!? Garage band is telling me there are 2 separate inputs available, but won’t put them on two separate tracks. Even though I select separate inputs for each track I create, ALL the inputs get registered on ALL the tracks equally.

I hope that made sense. Any help would be greatly appreciated.

Thank you!