These people call all the time and never leave a message nor do they ever stop calling. I kept a record of how often and when they called and they would literally call back to back times minutes apart all day long. I'm assuming from the length they are going to be annoying that they must be some sort of bill collectors but I have no idea who or for what. I finally used call block to stop it as I never have found out the name of the company calling or why they call. They may be a bill collector service but I have no idea for what. Occasionally they call from other "extensions" but it still says Manteca, CA on the caller ID so I know its them. I hope someone else can find out who they are since I haven't been able to.