Don't know what BT internet is, but have you tried using the ZOOM in your tools up top? Also sometimes using my center scroll buttom on my mouse, the text decreases in size something terrible. It comes back to normal when I reverse directions on the scroll.
Inre emails, I've used Yahoo Classic for several years now, but every time they upgrade their email system, I've lost all my contacts. Complaining to Yahoo''s been of little help getting them back. This last & most recent update by them does ask if I want to upgrade - with the clickable option of saying "no." Because I've written them about my losses without any fix from them, again I'm saying no thanks, but they will prevent many functions when using my old standby. Gradually I'm emptying out any special saves and will close the account. I'm switching email carriers since they at Yahoo haven't been responsive. I used to think theirs was the greatest, but now, to my way of thinking, they're fixing what doesn't need fixing; it was just fine as it used to be. Good luck getting your text size increased. I'm partially blind so it's an important feature for me too.