how I can unlock my phone

Only the carrier your phone is locked to can authorize the official unlocking of your phone, so contact them to see if you qualify & whether they offer unlocking or not.

There is no other way to get your phone officially unlocked. Apple can't/won't help you.

Then contact 3.

If you want your phone officially unlocked, & they charge money to do so, well, that's the way it is.

Ask 3. The carrier that your phone is locked to sets the rules/requirements for unlocking, not Apple.

It is what it is. Regardless of whether you like it or not, you will have to deal with 3.

They lied to you, plain & simple. Apple does not charge carriers to add a phone's IMEI number to the officially unlocked database, and that's all that Apple does.

Once you get your phone unlocked, find a new carrier.

Apple don't unlock phones so why would they charge! The carrier charges the fee not Apple. Apple simply updates their system after the carrier unlocks it. Your contract is with the carrier, it would be illegal for Apple to unlock it! Common sense! The carriers always pass the buck onto Apple.

unlock the phone

In case you didn't notice, this thread is over three years old now. I would guess the issue has been resolved by now.