Is there anything I can do to stop them attacking me?
I made a mistake and entered the building and now they're all after me. I even did their sodding DLC missions and helped them but the moment I sneaked into their base im their worst enemy. Wankers.
Any help would be appreciated asap as i keep running into them and dont want to kill them.
Thank you guys

As far as I know you have three options.

1) You can go back to a previous save before you entered the building.

2) You can use console commands to make them friendly

3) You can live with the consequences of your actions.

I did a little research and found these console commands, if that's the way you decide to go:
player.removefromfaction 00033089 (removal from Outcast enemy faction)
clearfactionplayerenemyflag 0001d3ff (clear Outcast crimes)
clearfactionplayerenemyflag 00030520 (clear OutcastGeneric crimes)
setally 0001b2a4 0001d3ff 0 0 (sets player faction and Outcast friendly)
setally 0001b2a4 00030520 0 0 (sets player faction and OutcastGeneric friendly)

What did you expect sneaking into their base. You would think they would be happy. They would likely shot you on sight.

Best option is to go back to any earlier save before you broke into their HQ. Or just take the consequences of your actions.