Inside of freezer bulging

We noticed that we were unable to close the door on the freezer section of our hotpoint mistral frost free fridge freezer. Upon investigation we decided to completely defrost the fridge. There is still a bulge on the inside. When we looked at the back of the fridge there was water collected in a plastic tray underneath. We tipped out most of the water and are wondering whether the bulge will subside. I cannot see how it will subside even if there is a build up of ice behind. Is it in fact a build up of ice that has forced the inside wall of the fridge to convex or could there be another problem.. Any advice greatly appreciated. Thank you