There are a few possibilities: first, you are just taking a very long time and it will come eventually if you keep doing what you’re doing and don’t lose patience; second, you are making one or more fundamental error(s) (probably regarding where and how you are looking during the exercise) and when corrected you’ll be able to do it; third, you’re just not wired to fly a helicopter and golf or fly-fishing will be better pursuits.
The first possibility will require patience. The third will require resignation (and a book about golf, or fly-fishing). The middle one is the important one, because the key is in finding a different instructor, ideally someone very well trained and able, not necessarily enormously experienced. In my instructing career I repeatedly came across people like you who simply had undiagnosed bad habits. With those corrected, they progressed. It’s good to read that your present instructor has some helpful qualities, but you need a second opinion. If the south of England is convenient to you I could make a personal recommendation, PM me if you’d like the info (it’s an ex-ETPS instructor with whom I’ve flown a fair bit; very sharp indeed).