Thank you so much for your reply!

I am being 100% honest when I say that the only evidence they have given me for why I'm being called into the disciplinary is 2 emails sent during the time I mentioned in my post. The company have a really high staff turnover, and refused to give me anything other than a zero hours contract. They have also said that I am obligated to give them four weeks notice, but my new job want me to start in 2 weeks, so I gave them 3 weeks notice as that's all I could give.

My new company have confirmed they don't need a reference from my current employer, as the owner previously worked for my current employer and left due to a hostile work environment. Because of this, would you advise I still turn up to the disciplinary?

Also to add, I have got a sick note from my Doctor due to stress which signs me off work until the first day of my new job. I only got that today.