I agree with MAWBROON, it does sound rather odd. Usually shops have to apprehend the person just outside the premises with the goods on them. I would do as other posters have said and ring the local police station to ensure the 2 officers are legitimate. I would also go to the CAB (Citizens advice bureau) for advice. Let us know what happens, I hope your predicament is resolved quickly.
What did you you think you would have by your current age that you don't?
Govt announces Ukrainian style scheme to bring thousands more migrants to UK
Yes why 12 days.? Phone the non urgent police number and voice your concerns. They will advise you what to do.