Sorry, I misunderstand your question. Do you mean you have a number deleted from Recent tap, but it was blocked? Or you want to restore the number from blocked list?
I think I got it, ok, a blocked number you received. But you deleted it on recent tab.
Try click 3 dots from top right on phone app->Block numbers
Sorry, I think it cannot be retrieved the deleted numbers from recent tab. I just curious, you said you blocked the 1800 numbers, if you click blocked the number, the blocked number should added to your phone blocked list. Not sure why it isn't there.
You can retrieve the deleted data if you made a backup on your Samsung Cloud or Google accounts. The steps for the Samsung account: Go to settings >> Accounts and backup >> Samsung cloud >> Restore data >> Select the Contacts option >> Restore.
You can also verify in your Google account: Open the Gmail app>>Tap on three linges in the top left corner>>Tap settings option>>Contacts. Then follow the on-screen instructions to retrieve the contacts.
It is not possible to retrieve the deleted data if you have not made a backup already in any of the accounts.
Your best bet is by looking at the detailed section of your carriers bill. It will show the phone number that you've called and the phone numbers that called you. Which carrier are you with?
