curtain bracket

Hi, I’ve been attempting to hang a curtain rail up for nice blackout curtains that are triple layered. However I cannot seem to drill any further than 1-2cm into the wall above sliding patio doors. Idk whether I need a stronger drill bit, or whether to not drill above as there are radiator...

I need to put up 3 curtain brackets (Left, Right, Centre) above a floor to ceiling new build window. Unfortunately previous owner drilled pretty big holes using Redidrive screws. The holes must have widened over time and I also want to use different brackets. The existing holes are about 8mm...