This happened to me two years ago. My kid turned off the dial on my fridge/freezer right before we left for a vacation. Came back to a putrid mess.
We seriously contemplated getting rid of the fridge (which was brand new) and getting a new one. But after about 3-4 weeks the smell eventually went away.
You just have to keep masking the smell. I found that cinnamon spray/candles worked the best. Also, buy a bunch of baking soda boxes and keep them in there.
Also, don't forget to thoroughly clean inside the rubber baffle that seals the door to the fridge. There are lots of nooks and cranny in there that can contain the smell. Pull it all the way out as far as you can and clean all around it.
Also, many fridges contain 'drip pans' underneath the unit. Pull off the grate and try to locate it and clean the shit out of it.