If there's froxen water back there where it's supposed to be bone dry, then the cause is likely the same blocked drain that others have mentioned. Get it running freely (a straightened wire coat-hanger should be in every householders' toolkit) and keep it clean. Off-hand I'd bet the OP's original defrost unfroze the blockage, and allowed the machine to cycle for a few days until the died peas, or lint or whatever that no one had actually removed got sucked back to their evil place and ways.Yes-- I had a fridge where the defrost went, after some googling it could have been one of several things, and all out of my skill set to fix. One thing that you can do if you don't want to wait the 2 days for the fridge to thaw (and your stuff to go bad) it to put your stuff in a cooler or plastic bins (to keep it cool and frozen), and then open up the back of the freezer portion of the refrigerator freezer. It's usually just a number of screws and plastic plugs. After it is open and unplugged you can then use a hair blowdrier or heat gun (rags and a bucket, maybe something in the way of a pick that you'll be vary careful with) to rapidly thaw the block of ice that is blocking the ducts and radiator bits. It's tedious but it will get the job done before your food thaws.
It's also not a 'permanent fix'.
No-auto defrost machines didn't have that customer-convenience stuff, never mind having to add it all in as cheaply as possible and keep it outta sight so they could claim they'd invented E-Z MagicFreez™ without actual frost ever occurring.
If you hafta write off your new fridge (and at least one repair call) inside of six years, buying second-hand, leasing or renting would seem more sensible.