I suppose someone who works in the field of advertising, could break down the exact differences between an offer and a promotion, however to the lay person, they are actually very close in meaning. It seems to me that what the bank is doing would be referred to as an offer since the customer actually gets a discount. Promotions can sometimes offer discounts in an attempt to promote a product or brand, but sometimes they just do an event or series of events to promote their brand. For example, I recently went to a Prince concert that was paid for solely by Samsung in an attempt to promote their new Galaxy IV phone. Since they completely paid for the concert, (which was free for the lucky few who won tickets), they were the only ones advertising at and in connection to the event.