Any one there to clear my doubt about iphone unlock?

I have a Iphone 7plus bought from Europe and using in different region (other than europe). I dont know how it was bought but it was unlocked to any carrier in my region. I was in doubt that whether it was unlocked thorough jailbreak but i could not find any traces of jail break. (As i google it is also said that unlocking thorough jailbreak was only possible in older version but not in newer). Finally, restored my iphone using itunes and installed fresh firmware. After doing so nothing new happened. (I mean phone did’nt get locked)

question:

1. is it true that newer version of iphone cannot be unlocked through jailbreak?
2. As i was regularly updating ios version, can jailbroken iphone to unlock get updated? Even if it get updated, wont it get locked again?
3. After restoring from itunes iphone didnot get locked, does it mean it was unlocked officially?
4. It it was unlocked through third party unlock service providers (not the carrier and apple itself), it still remain unlocked after restore?
5. and finally, if third party unlock service provider can get the legitimate code to unlock your device, why to pay them instead directly contacting carrier?