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My advice is to call, but for only two limited and helpful purposes.
One, to determine their identity, and two, to establishe a clear "initial communication" with the consumer, triggering their requirement to then send dunnning notice within 5 days.
I would not discuss the substance of the debt, simply request their name and address. If they provide it, you can then send immediate DV, thus putting a cease collection bar into force until they provide verification. If they dont comply, they will have to do so within 5 days by way of dunnning notice.