Flexi working agreement changed with new manager

I currently work in education. In 2012 I applied for and was offered a full-time post. Prior to acceptance I negotiated so I could work term time based on my children’s school holidays to balance the work and needs of my children as both children were in primary school. At the time the managers were happy to agree and I stated verbally on the phone that this was important in order for me to consider the role. This was verbally agreed. At the time and at no time after was I told that I would need to put in a request for flexible working then or for the three years in which this was in practice. The manager then was considerate and supportive. A year after working in the post almost half of the team who were on fixed term full-time contracts were offered full-time, term-time contracts but the contracts were not in line with the school holidays but rather in line with the days that the organisation wanted the staff to work in line with their business needs. The previous management left.

Since 2015/16 – a new manager who has risen in the ranks from the same post as myself decided that my working practice was no longer in line with other staff. She had a number of conflicts with staff when she was in the same role – personality clashes including with me and has made some threatening comments to assert her position.

I was told that despite the verbal agreement at the point of contract, HR have no record of it and therefore I would have to put a request in for flexible working. My immediate line manager had no problem with my work pattern.  The needs of the business have not changed.

Since the negotiations I offered to support on busy days and attend training days if required. This was negotiated reasonably satisfactorily before, but this year they have refused offering no flexibility. I have requested what impact it will have but they are not willing to discuss. I believe (retrospectively) that this is more down to the individual manager who is being consulted. I have worked with my union to try and resolve this and they believe that based on the past this individual is just being unreasonable and although this has been expressed, HR do not want be seen to be undermining her decision. Other managers in other departments have offered staff flexibility.

I have proven that I am very effective in my role. Since this new line management came in, I feel very stressed and am having huge problems with childcare.

I have exhausted all other options. Can you help?