You are absolutely right to be angry. Can you write to personnel and request a response within x amount of days clarifying your return to work so you can organise childcare? If not, they could delay your return to work if you can't get your LO into a cm/nursery at this late notice!
Hiya, I was in exactly the same position. I won a training attachment just before I went on ML to start as soon as I came back to work. I didn't know what I was expected to do until the week before. To be fair the job is very unpredictable, but it is really difficult if you're trying to arrange childcare. In the end I rang my line manager every day until I got to speak to him and get him to commit to something. It all worked out pretty well in the end as he'd been so disorganised he let me choose which days I worked and I can pretty much choose my hours so long as I do 7 days a fortnight and each day is 12 hours long. Sorry that's not much help for you, but I hope you get things sorted soon. It's definitely better speaking directly to someone rather than emailing. It's much easier to ignore an email that it is to ignore an irate person on the other end of the phone!