I had a similar issue with a rounded bolt head, in the end I had to take it to an engineering shop who had it out within a few minutes.
Google search for engineering should get you a few places local to you....
@twade76 started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
I had a similar issue with a rounded bolt head, in the end I had to take it to an engineering shop who had it out within a few minutes.
Google search for engineering should get you a few places local to you....