Telescoping pipe to Selkirk dsac down pipe?

[Zuluwhiskey8786]

Installed a Selkirk through the roof kit last year. It came with a dsac down pipe from the box that attached to the double wall pipe. Installing a new stove and the dealer told me a vent is telescopic pipe would work well. But I’m having trouble slipping over the down pipe. Any thoughts? I really don’t want to bend the down pipe up