Ending the O2 contract because I moved to another country

Hello, I sent a mail to the address for ending the contract for O2 on 20th March, 2020. However, I havent jad any contact from O2 side. Since I am going to close the bank account, I am worried that I have to pay from my country. Which is very difficult to do so. So I would like to know how much cancellation fees I should pay and how can I pay it.