No assistance regarding incorrect payment of City Taxes

I work for company A. They contract company B for human resources and payroll. Company B has forwarded in error city taxes since employment. I thought this was correct until they removed the tax at the end of last year. I contacted the city and they told me I am not within zoning and was never required to pay this tax. I was never informed of the change (removal of city tax) or error. After finding this mistake myself I contacted the city who only has forms available to file for a return for the past three years. In order to file for this amount of refund I need a letter from my employer. After a month my employer has not provided this letter (only insists on contacting Company B even though I clearly stated the city requests a letter on company letterhead from Company A only). Company B will not refund any of the taxes going back past three years which I can not file for. Company A has not provided the letter. Can I seek legal help for the letter and the refund? Was there wrongdoing about removing the deduction and hoping I wouldn't notice, which means I would have never filed for any refund available? Thank you.