Good afternoon. My son (18 months) has moved up to the number 3 teat in you range. But after simply a week, the teats tear and has to be replaced (on the exact same place). It is now the 3 pack that I have bought and had to be thrown away after a week. None of the other teats did this? His number 1 and 2 ones are still in great shape. Find this ridiculous, not to speak of costly!