I arrived at T2 last week and could not find a Telcel store in T2, that doesn't necessarily mean there isn't one. I ended up taking the shuttle train over to T1. Showed them by arriving boarding pass and they were fine with it.

Walk over the footbridge from the shuttle into the terminal but don't go downstairs, turn left while you are upstairs and the Telcel store is right there. It opens at 9.00am.