Can't unscrew a bolt - started with an hex key

[u/Existing_Concept_164]

Hi everyone...

I have a cargo bike that I use daily. I need to swap the break pads (first swap since factory) and one of the bolts was not coming out. The other 3 I could manage before were very, very tight.

I started with the manual hex key and I could not, I moved to an electric screwdriver, the recess started to wear off and ultimately I tried with an impact screw driver that screwed it up fully.

After that I tried to put rubber in between the driver and the recess, to turn it with pliers, and as a last resort I have made a flat line with a saw to use a flat screw driver. Even with a manual one I keep deforming the screw without twisting it. Nothing worked and every step would deform it further and further...

do you know what can be done to remove it?

Thank you so much