I am a teacher who needed to go part time after having a baby. They refused so I resigned

I am a teacher with middle management responsibilities. I recently put in a flexible working request to my school for part time employment upon my return to work after maternity leave. I gave them 5 months notice. I was refused. Point blank. I was not informed of any flexible working policy or any right to appeal. My case was discussed in front of the head and all the governors so even if there was a right to appeal, there wasn’t anyone neutral available to conduct it. I wrote to the governors saying that I was profoundly disappointed at their decision, I pointed out the current teacher recruitment crisis at present and that I regretfully had no option but to look for part time work elsewhere. They did not respond but my head teacher called me and told me she couldn’t change the governors decision. I am cutting a long story short here but in the end I simply resigned. I had no option, they were not going to negotiate. I firmly believe that they made it as difficult as possible for me to come back in any capacity knowing full well that I would be likely to go on another maternity leave shortly (I am 34 years old) They knew I would not be able to go back to work in my old full time role with a baby at home so it was ‘come back full time or not at all’ or at least that’s what it felt like. Not sure there’s anything I can do about it? (I have been in contact with my union who in the teaching world are usually the first port of call however, they were completely useless) Any comments welcome!