New sims are registered to old ID Apple accounts.

[Molly45]

I purchased 3 new SIM cards through sky, all SIM cards are used in android devices. Although a friend I was sitting with received an iMessage from the new number which is currently used in android device, the message stating some very offensive, threatening language. The SIM card is not used in a Apple device & has not been used in an Apple device, since purchasing it either. 

how do I find out if these SIM cards are still registered to a different person/still being used by someone else? 

[caesarome]

Are you sure this message isn't a scam one, just because it says it is coming from a certain number doesn't actually mean it is.