Media advertising agencies is an amalgamation of two different types of company that provide different advertising and marketing related services. Originally both services would have been housed in an advertising agency, which offered a full range of advertising services.
However most media departments broke away from advertising agencies after getting fed up with being marginalized at the expense of their creative colleagues. They may now be owned by the same holding company but there is no such thing as a media advertising agency as they will operate as separate entities.
A few full-service agencies still exist, notably in Brazil, where media agencies are illegal but a few continue to have success in the US as well.