After you file

I have an offset for DHS where I was overpaid funds a few years ago. So I know my taxes will be delayed. When I go on the IRS website to use the “Where’s My Refund” tool, it says they can’t find any information? I haven’t received my offset letter yet! It’s been 4 weeks since I filed. What can I do or who do I call to get more information about my refund? I am getting $2,009 taken but getting a refund of $2,900.