Leaving UK with unpaid phone on contract?

I have Iphone7 on contract with THREE mobile.
Already past half of the contract but i still have one more year.
The thing is that I'm leaving next month and I have to pay cancellation fee 380£ .
I was thinking what will happen if I leave without paying the cancellation fee and block transaction from the bank so they can't take the money.
Will they block my phone or what can happen?

The phone will be blocked and your credit rating will be destroyed.

You could be chased by debt collectors in the UK for many years if you come back.

They will do whatever they can LEGALLY, and you knew that before you signed up for a long term contract. See if you can FIND SOMEONE to take over the contract (in essence, to buy out your remaining time).

Why not ask your provider if you can convert your contract / service
to make the phone usable where you are going?

If that isn't possible, then you should pay the cancellation fee and get it over with.

Unless you are traveling into rural Africa or rural South America and never planning on coming back they will eventually catch up with you. At the very least destroying your credit rating, and possibly saddling you with debts many times that of the cancellation fee. You could even find that your ability to get a visa for certain countries would disappear!