I quit job b/c of unfair wk conditions 1:7 wk ratio & b/c employer failed to provide promised help. u/c on appeal. winnable?

Hired as head staffer supprtg 2 professionals, promised with growth more help will be hired; not done. Load grew to support up to 7; another staffer supported only 1 professional & not allowd to help me as not employed by company. I made interim & yrly complaints n mtgs w bosses about heavy wkload. employer took initial action; but failed to hire help. Yet add'l professionals hired, increasing my wkload; still no add'l support hired. I had to assume add'l responsibilities when prof'nal left; no recognition, no bonus, no raise, no thank u. Final stressful event, significant O/T errors by payroll service; several thousand overpd for over 2 years. I repaid OT, but quit bec of stress associated with wkload & trmt during OT snafu. how can I prove my case? winnable?