Need university to release me from clearing but they won't reply

I mistakenly applied for the wrong course through clearing, and there's no option on UCAS to withdraw. I've spoken to the university on their live chat but they said I need to email admissions. I've emailed admissions last week and still not had a reply. They don't have an admissions phone number open.

It's really frustrating as I'm wanting to apply for another course and can't until this course releases me. Is there anything I can do?