Hi,looking at your symptoms,it seems that you have suffered from noise induced
hearing loss and ringing in ear( known as
tinnitus).
Short course of oral Steroids and
hyperbaric oxygen therapy might help few patients if taken at the earliest (within 3 days) after suffering from such symptoms after exposed to a fire-work.
You need to have a hearing test-Pure Tone Audiogram,to check how much hearing loss you have.
You should avoid listening to loud sounds.
A
Multivitamin tablet and tablet-
Betahistine might help
If you are aware of pranayam,Brahmri pranayam might help.
Hearing Whistling /ringing sounds is not a life-threatening condition.It is a benign condition.So,dont worry much about it.Try to avoid giving attention to such noises.
Listening to White noise music(available on youtube) helps as the white noise tends to have masking effect on the whistling sound.
Hope this answers your question.Take care.