Why is my sim saying invalid sim card and asking for network unlock pin

[AC Question]

I brought my phone from cash converters almost 6 months and it was locked to Vodafone I think so I had it unlocked in a shop near me for 25 quid the shop now has changed owners and my sim worked perfectly and worked perfectly this morning until my phone died earlier so I plugged it into charge and when it was fully charged I switched my phone back on and it came up asking for thr network unlock pin and a notification saying it's a invalid sim card it's a Samsung Galaxy s6 edge so I can't remove the battery please help

 

[belodion]

Are you sure it was a proper unlock rather than a dubious one that only lasts until an update?