Well if you have a tablet, you can still do it. They give instructions on how to remove it right on the Unfollowspy website.
Try here...
http
/www.unfollowspy.com/removeaccount.html
It says right in the top portion of the page, under step one.... "Login to Twitter on a desktop device i.e Laptop, Tablet or PC "
So you can do it on any of those. Although it is probably easiest to do from a Laptop or Desktop.