technical support

If it is this one: mophie 3-in-1 Stand for MagSafe Charger - Apple then no you are not missing a piece you just haven't purchased it yet. You missed this part in the description: "Just install your MagSafe charger to the stand ..."

You need to purchase this: MagSafe Charger - Apple

You don't, you are past the 14 day period for a refund. Apple does not maintain service replacement units for non-Apple products, you need to click on the link I provided to you and contact Mophie support (Zagg owns Mophie). What is the model number of your 3-in-1 charger?

Contact Mophie support.

First, this is a user-to-user technical support site operated by Apple, you did not buy anything from me.

Second, if you purchased it within the past 14 days from Apple you can return it for a refund. Otherwise you get support from the company that made the device.

If you are past the 14 day refund period you cannot return it. You will need to contact Mophie support to get the missing piece. Mophie makes a number of different chargers, if you are referring to the Apple Watch part of the charger some models do not come with the charging puck/cable, you use the one that came with your Watch.

I don’t know, what did Mophie support say when you contacted them?

https://support.zagg.com/hc/en-us

Again, which model 3 in 1 is it?

https://support.zagg.com/hc/en-us