I went back to Vodafone for help blocking 188.8.131.52 on the modem but they have come back with "Your query in regards to the advanced settings in your modem is unfortunately unsupported by us, however, the manufacturers - Huawei, will be able to provide the technical support you need to resolve your issue. Their contact number is 0800 451 199." I have spoken to Huawei and they say the device doesn't support blocking this DNS.
I could replace the SHG1500 but it is new and shiny, and I'm cheap. I have my old VF modem still (an older Huawei) but I'm reluctant to mess about with my main service to the family. I'm thinking of adding the old Huawei as a secondary WiFi source and hopefully blocking 184.108.40.206 on it. I already have a seconday Airport Extreme for WiFi but it doesn't allow IP blocking.
Can anyone offer advice, please?