I work for a major, well known retailer (office based)(clue in my name)! 
When I took the job (full time), I knew I would have to work every third weekend, which I was fine about. I took the job because my ex said he would help out with DD (3.6) on my working weekend. He has now withdrawn this offer 
So, I've been relying on family and friends to look after her, but I feel like I'm taking advantage now, my parents are 70, not in the best of health, my SIL works full time and has her own two kids. Other friend works and has two kids.
So I approached my manager and asked if I dropped to two days a week, could I lose the weekends. They went away, discussed with other managers etc and said yes. Foolishly I didn't get this in writing, only verbally but was told all along it was agreed!
So I'm given my start date (in two weeks)and cancel my daughters nursery days. Today I get called aside by my manager, (I'm expecting to sign contracts etc) they said another higher level manager has decided its not acceptable and said I can't do the two days, as I have to do weekends
Apparently some other girls in other departments asked to do the same and they were told no, so I can't do it. However, my circumstances are different, I know they are not lone parents. So surely, the decision should be based on individual circumstances, not a group thing?
So any ideas where I stand on this, I'm so naffed off, I'm going to speak to the person who has changed the decision and ask her what she based her decision on? But how do I go about it, what do I say etc? What rights have I got?
Thanks