The email (that everyone with a Sumup Reader received) plainly says that if you don't actively opt out of this then you are getting a Master Card and all your future Sumup Payments will go into your new Sumup account.
If you ignore the emails then you have not opted out, so Sumup will have decided that you are happy to have your money lodged into your new account and your new Master Card will be on it's way to you.
You can still opt out of this, but I don't know how, as I opted out when I received the 1st email.
They are Debit Cards as far as I can see Watty. Just means less potential for Fraud.