There appear to be grounds to at least consider the possibility that this person was not, in fact, banned for being afk at the bank, but for conduct that happened earlier. Being afk at the bank just happened to be what he was doing when action was taken.
I think there is no further need to discuss this here. If the player concerned has not, as has been claimed. received a communication from EA detailing the offence he should email customer service.
Stratics posters can not help you further.