Many cells have problems growing in high O2 conditions (2% O2) and do not thrive due to hyperoxic stress. Try culturing your cells in the Petaka G3 cell culture cassette. This low cost cassette provides low, in-vivo levels of O2 and automatically, perfectly balances CO2 and pH levels in your culture. It provides the most physiologic conditions of any culture device. Your cells may not grow for other reasons, but before throwing them out or giving up, it would be worth trying the Petaka, it has solved a lot of problems like yours for a lot of researchers.