So your car failed. Bummer. You now have three options: pay the daily charge, upgrade your car, or move to the countryside (extreme, but valid). The daily charge in London is £12.50—which is like buying a fancy coffee every day, except the coffee comes with shame.
If upgrading, consider selling your old car to a dealer who exports them to countries without ULEZ. Your car might end up in a beautiful place where pollution is a fashion statement. We call this “the circle of automotive life.”