T cut removes staining caused by rusty water running on paint.
This gives the impression you've removed some of the rust but really your just cleaning the paint.
Yours looks like the rust has broken through the paint surface and the only way to remove it is to remove the paint and rust back to clean shiny metal.
You could paint the frame yourself using aerosols if you can strip the components and re build it your self.
A blaster could strip paint and rust or if your skint you can do it with sand paper or stripping discs mounted in a drill.
Have you had a quote from a powder coater?.