By the way, you didn't say "who" is mailing the check? You only said "they claim", but we don't know who the "they" are. There are a couple of possibilities.
Does the IRS website say it mailed a check to you?
https://www.irs.gov/wheres-my-refund
Or did you choose to pay any fees out of your Federal refund, and it's the third-party processor (SBTPG) that's mailing a check due to a rejected direct deposit?
