How do you get out really heavy duty bolts (like a wingback bolt I think)?! General problems, solutions, information and advice on fixing to walls of all kinds

[Newbdiyer]

The old owner of my house had these installed to mount his TV bracket. I don’t know what they’re called and have no idea how to get them out. I can’t hacksaw them off because of the angle to the wall and have tried drilling in (making a big hole around them but they go deep into the masonry. Any ideas gratefully received!!

[Newbdiyer]

I thought I’d added an image but I hadn’t - here it is!