They can alter course content - and even cancel them - whilst people are enrolled and studying. However they should be offering you another way of getting those 30 credits, otherwise the course will lose its accreditation and they wouldn't be able to run it at all.
Contact your course leader as soon as possible to find out what they've put in place as an alternative. Also, contact your NUS reps. They need to be aware that students are being disadvantaged.
Thanks guys, basically emailed them straight away and asked how they could justify doing it considering I had already registered on a course with 30 credits for the placement. What I was meant to do as I couldn't join on the course because I had missed 2 months already.
I also asked why they expected to recieve money for the course year!