Tax Exempt

I have been trying to get a billing issue resolved since January of 2018.  We have been charged sales tax, we are tax exempt - for a period of time the taxes were not charged, but they have shown up again - and have been consistant for the last 13 months.  I have spoken to numerous people on the phone - but DO NOT have time to sit on hold continously to have this resolved.  For such a large company - why is it so difficult to have such a common problem resolved ( I say common, becaused based on the issues I have read about in the Forum, I see I am not the only one.  I would like to have this situation resolved ASAP.