A lot of times features like silence unknown callers have an option enabled by default that lets you bypass it when you call a second time within X amount of minutes. On the iphones it's within 5 minutes with 2 calls (the first rejected) and I'd guess Samsung is similar. I'd look in your settings and disable that but keep in mind ANY CONTACT YOU NEED TO CALL will need to be a contact, as the bypass is disabled. That includes emergency contacts.
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I'm not super familiar with Samsung and how to do that so refer to what @dadibrokeit linked for a more focused response.
A lot of times features like silence unknown callers have an option enabled by default that lets you bypass it when you call a second time within X amount of minutes. On the iphones it's within 5 minutes with 2 calls (the first rejected) and I'd guess Samsung is similar. I'd look in your settings and disable that but keep in mind ANY CONTACT YOU NEED TO CALL will need to be a contact, as the bypass is disabled. That includes emergency contacts.