I just did that

You need to cancel it by calling Unifi (1300-88-1222), select language then press 1 , they will escalate it to the reseller to cancel it, the reseller normally do it slow and u need another call to Unifi (1300-88-1221) by press 1 - for portal team to remove ur account and they will send u the info on new username n pwd and then you proceed further but the info that used for previous registration will be gone including the phone number and date of installation.

not sure if the contact number middle with "88" , check urself

my pleasure