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Good luck with that one !!! It sounds to me as though you have, for whatever reason, entered the "wrong" code a number of times in succession and the phone has now "frozen" itself. Getting out of this situation can be achieved via an "unfreeze" code - more commonly known as an MCK code - and the very best of British luck finding anyone at any network who has the slightest clue what one of those is, or how to generate one. Very likely you will be pointed at Samsung who will point you back to Vodafone who will........ you know the rest.
My advice to you would be, unless you enjoy hours on the phone chasing wild geese, to take the S7 to an independent phone unlocking specialist and get it seen to there. This is likely to prove far quicker and less frustrating than trying to get front-line Customer Service staff to understand your situation and what is needed to resolve it.