iPhone 8 Plus shows "No Service".

This all began around Mar 6, 2021, when my iPhone 8 Plus showed "No Service". I, as usual, thought that to be a SIM/Carrier issue and took out the SIM, gave it a nice wipe, and turned on the iPhone an hour later. And kinda 'voila' cause it again showed up my carrier brand name with LTE beside it. But I often realized that there were call drops and occasional "No Service" text until around Mar 20 after which I had no issue whatsoever. That was until April 1st when I again started facing issues. I then doubted on my iPhone and swapped the SIM with my other iPhone (The other SIM was from a different carrier and both my iPhones are unlocked). Then I found that my iPhone 8 Plus showed the same issue while the iPhone SE 2nd Gen (my other iPhone) showed me the carrier that was present in the iPhone 8 Plus. I also noticed another thing that removing SIM doesn't show the pop-up "No SIM card detected" message and the top left-hand corner stays "No Service" instead of "No SIM".I tried hard to find the solution and tried things like resetting network settings, updating to the latest software, trying to manually update the firmware (it was already updated so I couldn't) and remove and reinsert SIM, none of which fixed the issue. I really don't know what the problem is. If anyone knows any home solution please do tell me, as the Apple store here is very far off from my home and is Off-route too, and I'm really trying to keep things at home due to this whole COVID situation. Hoping to get a reply soon.