I've asked Betfair if I can change my username and they said just go to your account page and change it!!!

That might be the case now but for people who joined several years (or maybe a decade) ago, you needed a username and now we're stuck with it, and fraudsters can potentially attempt to log in.
Only ever used a user name (decades ago)
It's difficult. The person I spoke to told me to change my username on the website. I told her you can't do that. Then she offered to change my email address. I had to explain to her that that's no use and I can do that myself anyway. Then she just advised me what I advised her - that you can't change your username!wearthefoxhat wrote: ↑Sat Nov 14, 2020 4:45 amOnly ever used a user name (decades ago)
If it's a real issue for you, I'd ask betfair if you could re create a new account with a user name and use the other security features too.
You're not trying to avoid PC, just improve you're security measures.