This is really shocking to hear, it would be interesting to know which university and course your son is on - although I appreciate you may not wish to disclose this information.
Obviously this is a stressful time for all of you as your son had previously been enjoying his course, and you were content in knowing that he was on the right path. In terms of the financial concerns, the case of changed course from 'contract' of university application should mean that the money is not lost - but this might take some time to chase down.
As the helpful above suggests, to make a complaint you need to complete the form here, using as much detail as possible in order to create a solid case:
https://www.oiahe.org.uk/making-a-compl ... form.aspx?
Whilst the complaint, and ensuring no money is lost, are clearly important - it will also be important to make sure your son does not feel completely dejected by this. Without knowing his course it is hard to help, but I hope that there is a possibility that he can find something that he finds equally interesting and rewarding.