Most likely, the MT isn't aware you're taking aggro. ALL tanks should have a macro for Provoke. An example is below. Note the 1 second wait and a second provoke being used. this is to ensure you don't get caught in the animation lock of a previous ability activating. Also, make sure you follow up the provoke with something like OP or a BB .

/micon "Provoke"
/p Provoking <t> NOW
/ac "Provoke" <t>
/wait 1
/ac "Provoke" <t>