Apparently three is issues with buying Cartel Coin via BestBuy at the moment. It should have been possible to buy from them as well as Gamestop for almost a month now but people are reporting about issues. Eric Musco have more on the story:
We are investigating this issue right now. In the meantime, we would recommend that you do not purchase Cartel Coins digitally from Best Buy. You should still be able to purchase physically from any location without issue but we are looking into the digital delivery issues that you folks are experiencing.
I will give you updates as soon as I have more information. If you have purchased a code digitally and not received it, please contact Best Buy and they should be able to assist you further. Unfortunately this is an issue with the retail purchasing and not something our Customer Support will be able to assist with. If you have purchased a code from a retailer you simply need to go to http://www.swtor.com/redeem-code and you will then receive your mini-pet via in-game mail.