With Calls being rejected could be various things, it could be a carrier feature or an application provided by the carrier that prevents certain calls from coming in.
I know from personal experience, with AT&T they had an application that was on the phone that would prevent certain spam callers, and block callers that were not on your favorites list or what not.
We also have Smart Call on Samsung phones, you may want to check out this particular setting on the phone to ensure this is not set up incorrectly or active - https://www.samsung.com/us/support/answer/ANS00088083/
The following may help as well:
Remove Block
From the Edge screen, tap Phone . If unavailable, navigate: Apps > Phone. These instructions apply to standard mode only.
Tap the Menu icon (upper-right).
Tap Settings.
Tap Call.
Tap Call rejection.
Touch and hold the contact. Selected when a check mark is present. To select all contacts, tap the checkbox (upper left).
Tap the Delete icon (upper-right). To disable a number on the list without deleting it, uncheck the box next to the desired entry.
Also you can try this to make sure this is off:
Tap Settings. Tap Call. Tap Call rejection. Tap Auto reject list.
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