I'll take a stab at what that means and I can see where they are coming from in process terms.
Starting with 2. because that is the most clear, I'd say. You say cancel and they'll do one of two things when they say arrange a refund.
A/ Initiate an immediate return back through whatever payment method you used and you'll get that in whatever time it takes for the payment provider to do that. A refund through PayPal, say, often comes with the communication that it will be in your Bank Account within 5 working days but in practice is often.
more or less immediately.
B/ They acknowledge the intention to refund but don't initiate the actual transfer back of funds until they themselves receive the returned shipment.
I suppose there is a third one and it's they don't do either and you have to take whatever recovery action necessary and possible according to how you've paid.
1. Is harder to decipher. The 10% voucher part, I'd deduce, isn't applicable to the one you may elect to get resent. By "next" they mean is for a future order you may want to chance at getting through untroubled, they aren't going to refund 10% off the one you are having resent.
It starts to get harder to understand what they mean after that. I'd say they are meaning that because of a number affected, they aren't necessarily coming back in logical order from despatch date but they are squaring their system by processing and resending based upon when they first sent it themselves.
So, an order sent a week later may arrive back before w=one sent a week earlier but they will hold that one their end and not resend it before the one sent the previous week. When that one comes back, it goes out before the first one they received.
Sending limited numbers, I suspect, is they only want one or two (figure plucked out of the air) in that Spain to Uk shipment process to have to monitor and try to get the paperwork done on.
Just my interpretation. I have no contact or affiliation with them.