I'm no expert on blueberries, but my understanding is that they take quite a number of years to become mature plants, but that once they do they crop heavily year after year.
You don't say how old they are, but it's possible you are being a little impatient if they are only two or three years old.
The general principle is to give them plenty of room to grow in quite big pots of acid soil, watered only with rainwater if you don't have acidic water from the tap, and you should succeed sooner or later.
I know that here they are grown in polytunnels and that they get large crops from fairly small plants.
Good luck, I'm sure you will succeed before long, but like all bush fruit and trees, these take some time to establish.