Can't reset security questions!

Hello,

I am trying to remove my Apple ID from my old iphone that I've given to a friend who is using it with a new number. I have managed to unlock my account and know my password, but I'm unable to answer my security questions to access my account. I can't receive a pin as I no longer have the same number/any Apple devices. I'm at a bit of a loss as to how I can fix this and would massively appreciate some advice if anyone can help! I am also out of the country for the next few months so can't receive calls/texts...

Thank you, thank you, thankyou in advance!

Kylie