to say no to work

[milewalker]

I started a new job 5 weeks ago, its a family run shop and there are 5 of us working there-one of them is the owners daughter. the remaining 4 of us are all part time and none of us have contracts of employment but I have a list of days/hours that are mine to work. since being there I have done extra every week.
tonight the owner phoned me to tell me one of the staff was ill and I have to do all day tomorrow. I was out at the time so my husband took the message and passed it onto me when I got home. I have no contact numbers for them so couldn't phone to say no I can't do all day so aibu to go in tomorrow and say I can't do all day but I can stay till 3pm?

I would list it but provide the other references, and say it was temporary work in the run-up to Christmas, if asked, but that their policy was not to give references.

thank you so much for replies and help. I will be able to start 2014 so much happier knowing I can leave this job and it won't be holding me back when it comes to application forms.

Just curious - were they paying tax and NI?

Just how legal was this outfit? (not wanting you to get into any trouble).

I have wage slips and the hours I've worked go to an accountant of theirs. I haven't worked enough hours to have paid tax or NI. I dare not ask to much-I just really want to get out asap with as little fuss as possible.