I bought a bottle 2 ...

I bought a bottle 2 months ago as I'm busy trying to introduce formula to my 3 month old.. I use the bottle soo little and the markings on the bottle are already fading.. I don't scrub the bottles I simply use a bottle brush and let the bottle soak on warm salt water for 5 minutes.. to clean.. I'm extremely disappointed I bought a 2nd bottle thinking it could just be a faulty batch that I received but now the exact same is happening with this bottle and I only have it a month .. both bottles were purchased at a clicks store .. I'm extremely disappointed.. this is my second child and with the first one I also just use the Tommee Tippee brand