How to activate Bluetooth?

It sounds like maybe there is a pairing process that must be completed with your phone, perhaps in the settings section of the audio system. You'll want to consult an owners manual to see if there are steps to take that you are missing. https://my.gmc.com/content/dam/gmownercenter/gmna/dynamic/manuals/2013/gmc/acadia/2013_gmc_acadia_owners.pdf