Not everyone gets the school they want their child to go to and where schools are full to capacity, unfortunately, they cannot take anyone else.
Nevertheless, you may be able to appeal the decision about the school your child is given. You can lodge an appeal for Schools that are maintained by the Council here: https://www.sutton.gov.uk/info/200439/school_admissions/1086/school_admissions_appeal.
Otherwise, you need to contact the school directly to ask for their appeal’s process. Please get in touch if you need help finding these details.