Only one order can be on a service at anytime... so it would only take one part of the bundle to not have completed yet and that would prevent another order...
there shouldn't be any charges for changing the bundle from the XS to the S... it is likely that when they processed the order that someone just clicked the wrong box in the list... but regardless it would be considered a change of plan within the same range... the same as you can move from S to M or M to L, you should be able to go from XS to S without an issue or any extra charges (other then the charges for the plan itself).
