Iphone 5S SIM Not Valid

I purchased a new unlocked iphone 5s online. Trying to use for first time - I'm in Israel now. When I put in SIM received message "SIM Not Valid". Looked up IMEI number online - carrier not listed. Took to 2 stores to try to get unlocked. One said it's AT&T, the other said it's T-Mobile. Contacted both carriers and they said not locked by them. Tried restoring phone via itunes - didn't help. Suggestions??