Many years ago I remember we had the same problem, I think when I was younger one of us accidently, partly trapped a coat in the door and it would not open again.

Anyway, my Dad, with one of us holding the handle open, pushed his foot against the inside of the door and it opened. (Basically applied pressure) Protect the door card with some rag first.

Obviously it may not work at all, but got to be worth a try.

Martin