If MySQL decides that using a key won't help performance, then it will be very stubborn about it. There's not much you can do to force it to use the keys.
With only 8099 rows involved, MySQL undoubtedly feels that just loading the entire table into memory will be better than using the index.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.