Can you get banned from buying games from CdKeys

CDKeys is an unauthorized seller. It doesn't have the worst reputation out of all of em' but it's still not authorized so the risk is still there. This is a list of some trusted authorized retailers from the EA help page (besides buying straight from Origin):

Note: Make sure you are buying from Electronic Arts as some of those sites listed also host third-party sellers on their websites alongside official sellers.

It's common on sites like CDKeys & G2A someone buys a bunch of keys in bulk with a stolen credit card and then sells those keys to the site. Eventually (even years later) a chargeback can happen which means EA can and will swoop in to void those codes. The account they are added to can become locked for violating TOS. So when you use these unauthorized sellers, be aware this can happen at any time and you are risking your account. These codes won't be voided immediately if they are fraudulent but it's also possible they are 100% legit... there's no way to tell. Just as an example, this happened to quite a few Sims 3 users a couple of years ago. Most of them purchased from eBay, G2A, but there were a few who used CDKeys.