Promax Render R adjustment seized

I have Promax Render R disc brakes on my Cannondale where the adjuster dial has seized, I've tried to use pliers to turn the adjuster but that resulted in the plastic covering coming off. I tried an allen key to turn it looks like the metal dead soft and has resulted in it starting to round off.

any ideas how I can get this adjusted temporally to buy me time to get a different brakeset?

Thanks very much

PS: what alternative could you recommend (i'd like to stick to cable discs)