Callcenters can be very busy at times. (posting during a quiet spell right now
)
Just be polite, advise them you have info that suggests they CAN upgrade, and be patient while they check.
If you start the call by being short tempered or moody, the agent is not likely to want to help you as much as if you were polite to them.
You could even drop a hint that he/she may have an Email regarding the upgrade.
No one likes a moody customer