Shorting plugs are what is used for crosstalk. The plugs that you have are dust caps! This is what a shorting plug looks like!
https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_3?dchild=1&...
https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_3?dchild=1&...