I had the alternator replaced but now nothing inside is working. radio, dash etc

maybe a bad/new/reman alternator right out of the box? how many DC volts on the battery terminals with the engine running, testing with a volt meter??

'IF' the battery was not disconnected prior to replacing the alternator .. The battery lead wire to the alternator was most likely shorted to ground at some point during the procedure and has blown a fuse or fuses... TEST FUSES!