R. Reader

I was replacing my roof, and the flashing for the furnace chimney was destroyed. The way the old chimney was put together I was unable to remove the flashing and vent cap. This caused me to have to take apart the venting in the attic. I'm generally hand enough, and manage to figure most things out once I get into them so I went to my big box store and bought a new vent (double walled to replace the original) Those items basically click together but when I went into the attic to connect it to the old work it wasn't configured the same. Please see the pictures below and let me know what type of adapter i need to make the old stuff connect to the new. Or any other work around? thanks.