Ugh, Christina!
First and most fervently, sending positive juju your way, in that your bone scan proves stable and steady, and that the pain is from anotHer lesser source.
Second, about your luncheon and subsequent letter from your work- it all seems so suspicious, the timing and your initial reticence to meet, but at this rate who knows and, does it really matter? If the letter was generated out of formality unhitched to your lunch, outta your hands. If your coworkers were grilled as to how 'sick' or debilitated you appeared to be then that's on them for playing their part, and that's on your employer for taking the low road. So be it!
Facts are facts: right NOW you have a formal letter in your hand. I personally think you've done right to leave messages--counts as 'cooperation', so, make sure you continue to respond as they call. Since you received a warning in writing, I would suggest writing as well. The phone tag thing is important to keep up, but now might be the time for your Onco to write a statement regarding your current status--that it is stable, neither up nor down...and politely renin them that your stable status means that you are atill disabled, according to the LAW. Any business could terminate on lawless grounds (cruddy business practice, to be sure) and hope that there's no litigation. So, if push comes to shove, you'll make it clear in writing that you're looking very forward and with great hope to the day you are able to return to your beloved job, and that you rest easy knowing your job remains available to you when that time comes.
They may then want to settle somehow.
It's prettty passionless, the way corporations and such work. And I'll suggest tHat now is the time to change out some (not all) of your emotion for mettle--stand up for you as a spoke in the wheel of society. Nothin' wrong with a little toughy attitude right now.

Lean into the wind, sister soldier, always, when it blows.

((Hug))

@A MyBCTeam Member - Karen says it all. Just be diligent about keeping notes and an email and paper trail of your communications with your company. Also, I see you are in Oceanside, CA. Have you exhausted your FMLA benefits? My company allowed me to take time off for chemo, etc. using the FMLA (Family Medical Leave Act) in addition to short term and long term disability. Just a thought.

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A MyBCTea...

@A MyBCTeam Member - yes way past FMLA. I took that for diagnostic testing once it was confirmed suspicious. Once it was diagnosed I finished all FMLA then went to short term disability for 6 months and have been on long term disability about 6 months now. I have now fallen off and have no further option to maintain my group insurance plan. I have drawn SSDisability. I did not file state as I was given incorrect information. Turns out that the insurance paying my disability was estimating what I was getting from the stat and lowering my take home. Now I have filed and will have to go through appeals process. Meanwhile my definition of disability by the insurance is changing so they want letters of exhaustion from the state or a letter d denile in my case and information from my oncologist based on my current condition. Because we are still running test the doc did not want to provide an incomplete assessment. I have talked to the insurance and at least they gave me an extended deadline for the paperwork. All exhausted!

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A MyBCTea...

Remember: These companies will try anything! If you have plenty of doctors behind you and it is documented that your employer was informed, that is all you can do. Just tell them, "I'll see you in court". Then hire a good attorney. NOW

They have to follow the law.

Really csnnot answer your question, but I have walked that walk. My emplorer pays for short and long term disability. I was on long term for a year during triple negative treatment. I got soooo sick, plus horrible side effects. After holding my position for a year, they legally medically let me go. They did inform me if I ever could work again, I could come back and start over. I now am on disability for neuropathy plus other side effects. Cancer.... the gift that keeps giving. Xxoo