This just happened to me too. Initially a few weeks ago I got the "denied" message on the T-Mobile submission/promotions page. So I called and got the $200 credit by a manual adjustment from an agent... then lo-and-behold, late last night I got the $200 bill credits text and just checked the status of the promotion and now it has changed to "approved". This could be fixed on their end in advance if they stayed within the SLA of their promotions. Not going to fight about an extra credit.
Out of curiosity - did you trade in at the retail store or did you send it back in the return shipment box?