can a uni just not give you your offer?

i got an offer through clearing (via email after an interview) and was told instructions to accept on ucas except now it’s been weeks and when i emailed to ask about a response they told me pretty much my application was expired and from what i gathered my offer isn’t valid anymore? that i’d have to do it all again, but it seems so strange. any advice? it was for january entry so i’m a little stressed about timing