my job had me on call for almost 2 weeks now and now they are calling me to ask me if i can work.?

I work in childcare and i was out sick for one week sick the next week they put me on call and then the following week again on call again well now today they called me and left a message on my answering machine asking if i can work thur, fri and next monday with no mention of anything else they are know for putting people on call when they want them to quit so they cannot pay them unemployment i am so fed up with them because they do this and now they are doing it to me!! they problay only want me to work because they are short as someone may have called out sick!! i am not sure what to do i know that i am not guarantee anywork next week either i am looking for other work and was wondering if they keep me on call and i don't go in when they call me (like today) can they fire me?? i am so sick of that job!!