unhappy

i bought a double pack nuk bottles for my 10 month old. the bottles which range from 6-18 months. i noticed my baby not taking to it. then i tried again, as i watched him drinking. he got frustrated and i noticed the milk was not decreasing on the bottle. then i realised the teat is too small. so i went to the store that i bought it. and now they say they cant exchange it. wow amazing. i am so frustrated at the fact that a product was bought now that it doesnt work.the nuk company cannot assist.very irate.