Hi,
Avent bottles drive me NUTS for this reason! I think its a major design flaw. Who has time to follow all their instructions with a wailing baby?! Anyway, I have found that if you twist the top the OPPOSITE way (as if to loosen it) FIRST, it usually works. I twist it three times the opposite way and then three times the correct way. Its not failproof, but it usually works.
Good luck! I really think Avent owes us a better explanation and a better product.
Michaela