No key for euro cylinder lock

Hi, my sister has just moved to a new house, the property had been a repossession. I think that the lock barrels had been changed as they didn't seem to fit properly, so I have changed these for new ones. the only problem is that on one side the patio door there is no key so I cant remove the cylinder plus some one as already had a go at drilling and forcing it with what looks like a screwdriver. I've had a go at drilling it but it is quite hard, don't suppose a lock smith could pick it now as it is well damaged. Any body got any ideas or experience? TIA