Major network issues on Note 20 ultra with T-mobile network and Cellspot

I live at the edge of T-mobile coverage on a hill. T-mobile provided me an LTE cell spot for years which worked fine with my Note 8 for the last 2.5 years. I bought my Note 20 ultra on September 6. Everything was fine for about a month.

Then, as of last week, around October 11, I started having major issues with phone calls and texts.


1) inability to make phone calls from the cell network

No matter how many times I try, calls don't go through.

This happens when connected to the cell network. I dial the number and it just doesn't go through or terminate. The same happens if I redial, no matter how many times.


If I enable Wifi calling, calls do go out, at least. However, there is frequently silence of 2-3 seconds that make it very difficult to have a conversation, especially when my air conditioner comes on. This is despite being less than 10ft from the wireless AC access point, and being connected at a Wifi rate of 866 Mbps, with the backend Internet connection being Comcast gigabit.


2)  inability to send texts when connected to either LTE or Wifi network

I use Signal with the confirmation on. Texts just hang forever when I send them. Recipients do not get them. Sometimes the texts will go out an hour later. Sometimes they result in an error.

The behavior with receiving texts is similar.


3) as instructed by a t-mobile tech, after rebooting my phone, and being located 6ft from my cellspot, it shows 4G or 4G LTE signal, and an "X" next to it, ie. zero bars. I can't make any calls, send/receive any texts, or use any data.


4) a reset of all the network settings on the phone did not fix the problem.


5) t-mobile did a "refresh SIM" on their end. It did not fix the problems.


6) If I power off the cell spot, all the problems go away in my home office. This is what I did for the last week while waiting for a replacement cell spot. But I then have only 0.4 Mbps speed even on the 5G network. In other spots in my home, I have zero cell network signal at all. I am in a 4600 sq ft home. T-mobile send me a new replacement cellspot. I just got it yesterday. All the lights on it are green. Unfortunately, all the problems described above are also back on my phone once the cellspot is on. The cellspot is supposed to improve cell signal, but in fact completely kills it for me instead with my phone !


At this point, I'm completely stuck with using my Ooma voice over IP phone to make phone calls. Without it, I would be completely SOL with making calls. I cannot reliably send or receive texts, since Ooma doesn't offer that service.


It is too late for me to return my Note 20 Ultra to the store. And I have already sold my Note 8.


My husband also has a Note 20 ultra, bought from Costco the same day as mine, and isn't experiencing the same problems, though he is not home most of the time.


It seems there is something wrong between my own Note 20 ultra and the cellspot. But I don't know what it could be.

I'm really at my wits' end.

Obviously I have been working with T-mobile techs on the phone on this, but they haven't been able to fix it. 

I posted my question to the Samsung forum as well at https://eu.community.samsung.com/t5/galaxy-note20-note20-ultra-5g/major-network-issues-on-note-20-ultra-with-t-mobile-network-and/m-p/2178139#M4773 .