Can I just use my old SIM card and put it in my new phone to use it?

Hi I'm a current USA boost mobile customer and I just order a new phone on there website and was wondering can I just stick my current boost mobile sim card in with the new device when it comes in?  I went to a boost mobile store and they told me I would have to get a new sim card and start a new plan and account all over again and will have pay 55 dollar for my new plan and 30 dollars for a new activation fee.  Is this true?  Or am I just being lied to. If so I might switch to metro PCS. Even though I love boost mobile a lot more.  -_-

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