MTSO holding back their top level MTs on purpose. - frustrated

This has been bothering me for many months now but I feel so stuck needing my benefits.  I can't change jobs because I rely on the medical insurance and can't afford Cobra while changing jobs. 

I love working 3rd shift and my job gladly accomodates; however, I'm constantly sold short because I'm left being the only 3rd shift MT most nights, expected to check queue on 5 different account log-ins to monitor TATs and logging in and out accordingly.  Obviously this cuts into my production.  When I brought this to their attention they told me they "didn't realize" and would look into a solution.  This was months ago.  Since then, I am not ashamed to say that I basically quit checking the queues for this reason.  I work one account until it runs out of work regardless if I have WTs with 8 hour TATs vs 2 hour out of TATs on other accounts.  Since then my pay has increased a minimum of $6.00 an hour!!!  As long as they don't say anything to me about this I'm fine with the way it is as long as there is work without me logging in and out all night between accounts. 

The thing that has bothered me the most is that after I realized that I've seen a lot of request for QC on accounts, I talked to my supervisor about letting me QC as a secondary when MT load is light.  There are times that there is tons of work sitting in the QC queue but very little in the MT queue.  She told me this was not possible because I was not a QC.  Okay, understandable, but with my experience of 13 years doing acute care, my 99.8% average quality score, why am I not qualified for QC when that position has a need?  QC is allowed to do MT when their work load is light, so why can't I do vice versa?  When I brought this up with her she said they are always sending out e-mails for "career advancement opportunities".  I have NEVER received a single e-mail.  So, I asked one of the higher ups why this was and her reply was that I am considered a valuable MT and it would directly impact the average quality scores on the accounts I'm working if I were to advance and that I have basically been taken off of the "advancement opportunity" list for this reason.  They literally took me off e-mail list because I'm good at my job.  Nevermind that I've been doing my job on top of monitoring accounts (team lead job description) since I've started here for only production pay!!!! 

I have no idea what I'm supposed to do about this.  I'm in a damned if I do, damned if I don't situation.  I basically have a supervisor who doesn't do her job and my pay is directly impacted, yet, I can't go higher up without badmouthing my TL and I just don't find that ethical (not that what they are doing is ethical).  I just hold higher standards for myself. 

Any advice on this situation?  I'm unsure of the words to say to get my point across.  I've been doing this job for way to long and too darn good of an employee to be treated this way.