You do understand the concept of co-equal branches of govt don't you? It means no one branch is above the other branches, they are equal. If Congress wanted to interview these people, they should have gone to the SC and gotten a ruling from them to force the interviews. They didn't, so there was no contempt of Congress.
Was it contempt of Congress that allowed Obama to block Holder from testifying during the Fast and Furious investigation? No, it was his legal right to do so, just as it was with Trump. Leave it to leftists to fail at understanding how the govt really works.