I just got a new 16 SEER A/C unit and I'm being told I can not use the 13 SEER A coil I also purchased, is this true?

Not sure why you would have bought a 13 coil with a 16 condenser. You will never get 16 from the condenser, maybe 13. Get a 16 coil to match and save money with the higher efficiency.

As ma0641 said, it may work but the best seer you will get is 13. For the extra money you paid for the 16 seer condenser, it is surely worth a bit more to get a matching coil. However, if it were me, I would opt for the cheaper 13 seer condenser to match your coil. It will take many many years for the extra three seer to pay for itself.