We fostered a dog like this one time, actually a couple of them have had similar behaviors.
What we did is feed a good quality food and then I made up a little dog stew: meat, broth, and carrots. I mixed the two together. I fed at the same time and same place every day. The first week was tough and I was sure the dog would starve to death! Our vet really encouraged us to keep it up. By the third week the dog was eating just fine and we could move on to other issues.
A month is not very long to have switched foods. Buy a good quality food and then stick to it. Makes sure that there is no other food the dog can get to.
Beneful is a great food and so are a couple others that our vet recommended. I can't remember the names of the dog food for anything at this point though!
These poor rescued dogs has been through it all. They just need someone to just be patient. Oh and the dog may need a bit of a long distance relationship while they are eating at first.
