I disconnected my air pod from phone as could not get working and then tried to pair again my air pods, They are not the latest versions and are about 2 years old

I disconnected my air pod from iPhone as could not get working and then tried to pair again my air pods and could not get phone to pair. I have charged them many hours and the charging light is green when I open at the case but turns red after case is open . They will not respond to trying to pair to phone again

bruce