Mites are usual cause of crusty ears in cats. If you are sure that there are no mites then other possible cause can be bacterial infection. First of all you wash ears of your cat with per oxide. After this use topical antibiotic cream or antibiotic spray which is more effective than cream. The treatment will respond within 2-3 days.
You can also visit to a vet to avoid further spread of infection.
You can also visit to a vet to avoid further spread of infection.