Hey guys,
Just tried replacing my gf's front pads on her fiesta and some absolute numpty grease monkey has rounded the bottom bolt on the caliper

.
It's an allen key bolt with a rubber sleeve around it.
What are my options? Ive tried smashing a size up allen key socket on it and it's having none of it.
Were not massively flush right now so a garage is the last resort.
Helps please