I can't access the sim card manager on my phone - it keeps crashing and now I have no mobile network access.

I have seen a simlar post and I am mirroring what was said before as there didnt seem to be a fix posted.  

I have an S21 ultra dual sim. I was traveling internationally and had the sim 1 slot turned off in the sim card manager so I didn't incur roaming charges. When I landed home I opened the sim card manager and turned off the sim 2. Usually I would turn one on before turning the other off, but I was so tired I turned sim 1 off, then the phone crashed - so I effectively have both sims turned off and get no mobile signal at all 

I tried to reload the sim card manager but when I tap it, it either does nothing, tries to enter the sim card manager and then exists before it can load anything, or gives me an error message related to call settings. The only way for me to load the sim card manager is to take both sim cards out. Otherwise it won't load it it gives an error and as soon as I put the sim cards back in, one or both, it wont allow me to access the sim card manager - it just doesnt load. 

Note: I hadn't opened the tray to swap physical sim cards in about two weeks.

Does anyone know what's going on or how to get my sim card slots working again?

Things I have tried:

- Multiple resets

- swapping out sim cards

- swapping which sim card was in which tray

- doing a reset in all network connections

- booting into safe mode

Anything else someone might be able to suggest to fix this issue?