rotten maize meal

i bought 10 kg Superwhite super maize meal @ shoprite lebowakgomo,am not happy with the product i bought.i foun some hard greenish stuff in my maize meal,its like it has veen stored for so long as the expiry day is still valid.I had to sieve the maize meal so that i can trow away the damaged one,i could not throw the whole half of the bag coz it was the only maize meal i have.I could not take it back to the store coz it is lil far and i lost my slip.