Had a similar problem when I purchased the old family homeplace. You can rent an ozone machine and let it run in the affected room for about eight hours. You must stay out of the room for the entire time it is running, I would suggest leaving the house for that time. Ozone can irritate your throat and make you feel an "itchy" sensation in your lungs, but is relatively safe. This is the method that hotels use to get smells out of their rooms and matteresses. An ozone machine is about the size of a microwave.