Excess HSA contributions still in account after deadline for timely withdrawal

I signed up for Medicare in 2018 while still employed. At the time I was unaware I was no longer eligible to make HSA contributions .  My employer continued to make contributions & I later complained that they should have stopped and/or  provided more information during Dec 2017 when elections were being made for 2018.  My complaint was denied; employer stated (probably correctly) that I should not have relied solely on info provided during election period and the complaint took quite a while to be resolved.   Bottom line: I did not withdraw the excess contribution by what I think I now understand as the latest possible date, Oct 2019.  I started to pay an excise tax of 6% each year, and I'm now wondering if there is any way to "cure" this error.   Every article I can find speaks of withdrawing excess contributions for the *prior* year (and perhaps earnings).  None make it clear if it is possible to ever stop paying the excise until the HSA is depleted.  Please clarify: am I really stuck now?