IRS will always write. IRS never calls. Above all IRS will never threaten you, IRS will never make an offer to settle your case over phone. Whatever IRS does, it will be in writing, and you will get a chance to contest or appeal your case with facts.
IRS has enormous resources and it will find your correct current mailing address if it needs to reach you.
If someone's calls and threatens you over phone with an arrest or big fines or punishment, it is a scam. That is not how our American justice system works. Don't fall for scams. Scams support criminal, terrorist groups.