Luno introduced support for BitCoin Cash accounts in 2017. While these accounts are importing to 22seven, they are currently displaying the incorrect balance, as Luno have not set an exchange rate for these accounts on their API (the direct data connection between 22seven/other service providers and Luno). As soon as this is sorted by Luno, these accounts should display the correct balance in 22seven.
In the mean time, we suggest getting in touch with Luno to request they make this change on their side.
Sorry for the inconvenience!