Upgrade 10Mbps to 20Mbps nightmare

I have been trying to upgrade my Uncapped Home Internet 10 Mbps to Uncapped Home Internet 20 Mbps with no luck. One agent tells me I cant upgrade have to cancel 10Mbops and get a new contract another one tells me I can upgrade. Their agents are contradicting each other and last time I was told to contact some other company Mondo or something like that. Am not sure what to do as calling them is a nightmare