The 855 area code is a toll-free area code for use in the United States and Canada. It’s just like the 800 area code in this respect. It isn’t tied to a geographical region within North America, and it is used by a lot of legitimate businesses. It is also used for illegitimate purposes, so its safety is debatable.
Sometimes you answer the phone and just hear a beep, and that is almost always the result of a computer system. The computer is trying to connect you to another phone line, and for any number of reasons, that connection failed. Usually, this is tied to robocalling, and the reason for the call can vary widely.
In North America, 324 is a reserved area code, which means that it is not currently in use in any region. While no country used 324 as a country code, Belgium uses 32, and Ghana uses a prefix of 233. Both of these can end up looking like they are a 324 area code when a caller ID has formatting limitations.