Unlocking Question

Hi all, I recently sold my old iPhone 7, it’s locked to vodafone. The buyer has said they need my mobile telephone number to unlock it to switch it to EE. I’m nervous about giving out my number to someone I don’t know as I am using my number on my new phone. They say that they’ve been into a Vodafone shop who has told her she needs my number. Is it safe to give out my number or is this a scam? I really have no idea!