Assurant Tmobile Vicious Cycle

So I had a lost/stolen phone, i put in claim with assurant.

October, 2023 i now have an $840 charge on my bill because they are saying I didn't return the phone.  I call Tmobile, it was lost/stolen, I can't return something I do not have.  They say call Assurant.  I call Assurant they say call Tmobile only they can remove the charges and it would take 1 to 2 billing cyles AGAIN

November 2023, .I call Tmobile about Assurants erroneous charge to my account, they didn't receive anything from Assurant and I was to call them.  Assurant says the template was sent to Tmobile, I call Tmobile back, they didn't receive anything.  But they will look into and call me back.  NO RETURN CALL.

December, 2023  Again, I call Tmobile, not to worry they will get in touch with Assurant and get everytingn taken care, in the meantime I can set up a payment arrangement.  So, I did.   it would take 1 to 2 billing cyles

January, 2024  I call again, to both same cycle Tmobile call Assurant, Assurant call Tmobile.  They will change the payment arrangement.

Yesterday, January, 2024..NOTHING WAS DONE by either company to fix this problem.  I learned from an Assurant employee that they had shipped 2 phones to replace 1 phone, i only received 1 phone and still the charges are there  Still Tmobile says to contact Assurant and Assurant to Tmobile,

They won't give me another payment arrangement!  They won't fix the problem.  Assurant is a subsidiary of Tmobile so what is the communication problem?

So I ask, please, what can I do?  Other than when all this is settled get rid of Tmobile and Assurant.