The KJW "Canadian legal" Glock comes in 2 versions - 1 with a metal slide and one with plastic. The plastic slide version being significantly cheaper than the metal one.
Seems to shootsoft may have accidentally sent you the wrong gun. From reviews on this site, it's not unusual at all for them to mess up orders. If it's new in the box and unused, MAYBE they'll correct their error. The fun part will be getting them to acknowledge that they made an error in the first place and then to get them to make it right at their own expense. They have a horrid reputation when it comes to customer service, even when they've been clearly proven to be in the wrong.