Sim lock unlock

Hi,

I received an Iphone 12 Pro Max as a gift, It was bought Prepaid from T-Mobile USA.

but i live in the Sri lankan, and the T-mobile sim card is not available there, When i want to use the available sim card in my country the IPhone shows it’s sim not support, and in the setting, and carrier lock is “Sim Locked”.

I don’t know how to unlock the Phone, In the T-Mobile & Apple website ,says you should contact to unlock. I wasn’t successful to call the T-mobile from the contact page numbers.

and as i don’t have T-mobile sim i couldn’t Signup or signin to T-mobile.

The problem is there for T-mobile app, In the Iphone after the installation the app will kick out and doesn’t open, and in the android phone is just the features that in the website.

And as i figured out there isn’t Email option for contact.

What should i do?