How not to use WhatsApp to service customers

What a nightmare! I've been a client for several months and just wanted to move my setup to my new premises 4 houses away, about 100m. It was promised for 14 November, eventually, after lots of conversations with numerous agents (who it appears are only taught to apologise; nothing else, as they certainly don't provide any service) the setup was installed 9 days late on 23 November. However, I'm getting a much lower speed than I had before (50mbps compared to 500mbps before) and I cannot get hold of anybody to fix this, in spite of holding on with their ridiculous and extremely frustrating WhatsApp agents.