How long has he been on the ranitidine? We were told to give it at least 2 weeks before we could expect improvement. Mind you, we did actually see dramatic improvement from C within about a week. The spilling didn't decrease so much as it stopped causing him pain. If your bub has had reflux undiagnosed for a while his oesophagus etc could still be healing, so can take longer to notice improvement.
Good luck