You probably need to call. They may be taking more time but often their actions are quite prompt. If it was so documented in the PNR a UA rep can retrieve it (I think it takes some time when more than 48 hours have passed since the last flight) and read the documentation to support you. In that confusion, a chance would seem to exist that you were rebooked on NW without actually being classified as VDB. Might as well start dealing with it.