COMOTOMO bottles

Hello, I bought Comotomo bottles and after like 3 months of use, the nipples turned cloudy and like oily. I wash them and sterilize after feeding and it just got worse and worse even the bottle feels sticky, any recommendations on what to do? I even bought a new sterilizer cause I thought we were not washing them properly ? . I had to buy new nipples and bottles and the nipples are becoming cloudy and I've been using them for like a month. Any comments?