I seriously think it's just the A series phones that have issues. I bought 2 of them last year, the A20 & the A10, for my husband and I. Used them for about 2 weeks before we really started wondering why No one was calling or texting us at home unless it was thru Messenger. When we started testing our phones to see if we had service, we could not get a call or text to each other at home. If we left our house & go 2 blocks (literally) both our phones would blow up with every call/text/notification we should have gotten while at home. If i put my sims card in my old phones then i had zero problems. I got told it was my carrier's issue but i proved that wrong simply by switching phones & service working. I've used Samsung Galaxy phones for years now & have had no issues with any of them Except the A series. I will never recommend them to anyone. But i suggest looking for you a new phone would be the best solution to your issue with your A21. I always see good deals on phones thru facebook if you have an account to start there. You can even filter your search for only Samsung Galaxy phones.
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