12 year old Terrier Poodle mix's chronic dry cough

[Nutterscooby]

He suddenly developed a persistent hacking cough having 18-24 episodes day and night. Kept everyone awake. Cough improved immensely with antibiotic. reduced to maybe 4-5 episodes per day on the first round of general antibiotics, but went came back 4 days after 1st round of pills ran out. Second round of respiratory-specific antibiotic worked even better maybe 1 or two coughing episodes every other day. Also improvement in playfulness...less grumpy. Vets are stuck on the idea that my dog has congestive heart failure because of a heart murmur and enlarged heart. But he was diagnosed with that heart murmur and enlarged heart 8 years earlier. No coughing until the last 2 months. Also, antibiotics would have little to no effect on congestive heart failure. Dog gets much better with antibiotic but it comes back after the pills run out. This is getting ridiculously expensive. Nearly $1K in vet bills over the last 40 days.