TMobile signed me up for wrong plan; how do I change?

TMobile signed me up for a plan based on what they said was available spots on my local tower.  Turns out there's spots for my desired plan.  So I called Tmobile back, and they said they had switched me to the desired plan.  Bill comes, and I'm still on the undesired plan.  Tried calling but on endless wait and don't trust what they'll tell me anyway. ¿Qué debo hacer?