Hi,
Sorry to be the bearer of bad news but some dogs no matter how hard you try don't come back. I own a 4 yr old kelpie who is absolutely brillant in every other area but if she gets a certain distance away she will not recall, she will basically run until she hits a fence. I now realise this and limit the areas outside my horse property to where she can be off lead. Your dog may have the same problem.
It is an extremely frustrating problem.
Mel