In January, I made the decision to hand in my notice of resignation for the sake of my mental wellbeing - the stress became too much for me to bare, and after a number of attempts to address the issues with management, I gave up and handed in my notice.
My employment contract requires me to give at least three months of notice, which I agreed to from the very beginning. The initial agreement in my notice of resignation included a leave date in April, three calendar months from when I handed in the notice. After a number of meetings to discuss further, I was asked to extend my notice period to June, meaning I would be giving over 6 months of notice. I agreed to this in writing. I agreed to this because I was told (verbally, during the meetings, not in writing) that management would try to make things better, and for the first two months or so, things did get a little better. But it's been over four months and I'm at a point where I feel I can no longer continue to serve this notice period.
I have already served the notice period that is required by my employment contract, so the notice I am currently serving is voluntary. Am I required to see it through? Can I leave without serving the rest of this voluntary notice without breaking any rules?
I understand that leaving abruptly will likely cause problems for my colleagues. Please understand that there are a number of reasons for why I'm at this point. I've worked at this company for over seven years, with the last five being in a senior position. My job has gotten so bad in so many ways, I simply cannot continue. I have already accepted an offer for a new position and I have the means to financially support myself until I start the new job.