Changes to agreed flexible working

[Whatutalkinboutwillis]

I work rotating shifts on a part time basis but for the past 3 years have had a agreement to have the same 2 set days off a week. The other mum in the team works opposite me and I work her set 2 days off.

I put In a formal request for this at the time and was verbally told yes. Nothing was in writing in their part and my contract was not changed.

Fast forward 3 years and they have decided to change the roster and will not give us the set days off. They also have us working 2 weekends more than full time staff.

My question is if we have had set days off to assist with child care after putting in a formal request can they do this? Also in a team of 4 people 2 part time 2 full time can they roster is on more weekends?