I bought a new iphone from Apple - unlocked, used and am using it with Koodo, but want to use with a different carrier in Europe. But the new sim won't activate- says it is locked by previous carrier. Why did Koodo lock my unlocked iphone??
If you bought it unlocked from Applein Canada, you will need to go back to them. Apple manages the lock state of iPhones, not the carrier.
By chance did you buy your phone in the USA? Those phones lock to the first carrier SIM inserted.