You haven't been banned, your orders are getting cancelled. Banned means you can't even place an order. Try ordering a fridge, bet you they'll let that one through
I stand corrected, so far every order I've made has been cancelled minutes later, this happened today and 2 weeks ago when I last tried to place an order. The official reason is it can't verify the billing info but the billing is fine I even asked amex just now just to confirm and they said everything is good to go.
UPDATE: Try logging in, this whole time I was using guest checkout, I logged in and so far so good.