Changed my contracted hours

[BB41]

Good Morning and thank you for having me , I work in Dot.com started as a delivery driver but due to an incident working a late shift I requested a change to click and collect as a pod driver  evenings and all day  Sunday

My contracted hours are 17 hours but have been informed today that as ``I only work evenings they can only offer 10 with other time made up with over time if available.

I've always helped out whenever covering other shifts at short notice so feel pretty upset about this.

Can they do this? . I only started in December so don't want to leave as I do enjoy it