I received a CP13 on my Turbotax return, saying that did not accept my $600 stimulus claim. I qualify in every way for the payment. Do I refile?

Only the IRS can answer that (they do not notify TT) , but the income limits are different for each of the 3 payments.

Or perhaps their records indicate it was already sent to you.  Some of those went out as debit cards, which taxpayers may have thrown out as junk mail.