Should I leave after hostile treatment in pregnancy?

I work in an estate agents office and have been top performer several times. I informed my manager when I was 11 weeks pregnant, but no health and safety forms were completed until several months later. I asked to reduce my hours, using my annual leave, but was told this would not be an option.  The office temperature was very high and made life very uncomfortable for me and long hours were a big strain.  I ended up purchasing myself a fan to help regulate my working temperature – the office was sometimes as hot as 26 degrees. A bullying culture developed which I informed my manager about. Following this my doctor signed me off for two weeks. This led to a meme being posted on Facebook about covering my shifts and pressure on me and my partner as Statutory Sick Pay isn’t great.  I requested to be signed back to work a week early, but was told I had to cover an extra Saturday straight away. After returning to work I was made to sit at the back of the office (where no walk-in customers can see me). I had derogatory comments about the pregnancy from colleagues and about having time docked for ante-natal appointments. I felt there was no concern for my well being and I was mocked if I brought up pregnancy-related issues. I am now on maternity leave and have been told that part-time work in my post is not possible. I feel like I’m not welcome now, let alone if I want to come back after maternity leave. Should I put in a flexible working request after maternity leave  and wait to see what the response is or just leave? I have another job lined up.