megane mk2 read discs removal :-(

hi all just tried to remove the rear discs on my megane mk2 but shes fighting back .i cant get the bloody brake carrior of to romove the disc .got the pads off and thats it i even have the E16 socket and its just rounded off both bolts .so there gona need cutting of now :forehead: i couldent even be botherd to try the other side .so what should be a 45 min job turned out to be a right nightmare ...does any one no what size bolts i will need after i have cut them off as i will not be using the same bolts on the other side even i can remove them ok