How frustrating! So many sets of tubes does seem to be excessive. It's not working so I wonder why they want your child to keep doing this. You've had his adenoids removed - did that help? Or is it too soon to know? I'm not sure how long it's been since this surgery was done. But tubes don't solve all the problems - they are not a cure-all.
Have they been specific about what is causing the blockage? As the poster below says, wax can be an issue. So is fluid, and so is general inflammation.
I've seen so many families whose kids' tubes have fallen out. I work in food science and there are thousands of families who use cellular nutrition to boost the immune system and reduce inflammation with a food-based formula (not an infant formula, but a supplement). There are plant-based peptides with strong anti-inflammatory properties that also help with epigenetic repair; that is, repairing malfunctioning cells. It's very heavily researched in a number of areas, including cancer research (stopping the spread of abnormal cells and slowing/'stopping metastasis). It's heavily used in feeding stations around the world for severely malnourished children. I've spoken with the doctors who document the improvement of a wide variety of conditions in the children they treat, so it's definitely a safe alternative. It's not an overnight fix though, and it's not a cure for everything. But it doesn't conflict with medical procedures or medication either, so it's an alternative. There are guidelines for looking at supplements though: don't believe labels (google the problems with Whole Foods and GNC), look for patents (which means the label ingredients have been verified), look for the reputation of the chief scientific officer, and more. Let me know if you want more info on guidelines for evaluation.
I hope you find an answer! I'm sure this is making you crazy, and you are worried about his hearing long term as well as his discomfort short term as well as anesthesia used for procedures. Some kids mature out of it; others just don't. Sending you good wishes and support!