NMLS#, I see no reason. This is clearly after they have acted as an MLO and they aren't negotiating terms of the initial loan.
I would think of how you're going to document this collection effort, and also, I would treat it the same way you treat leaving a message on a phone. You don't know who might be on the other end of that phone, so probably best to be vague and just request they contact you.
Hope these are work-issued devices they're doing this through as well! I think it's a sticky area and would personally try to stay away from it.
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Someone's about to get horned!