Incorrectly installed Broadband and no connection

I had Virgin installed incorrectly installed on 1/4/25 and it never worked properly. I messaged and called several times to report and they could see a problems in Area 20 for 48 hours but could see more issues with connection and were sending an engineer 10/4/25 between 12-4. I took a day off unpaid to wait for the engineer and they never showed up. At 2pm 10/4 I tried messaging but with poor connection was unable to get anything resolved as internet was cutting out. I eventually got through on cancellations and made another complaint and said I’d like to leave under the cooling off period (day 11). I was told there would be no charge as I’d never received the service. I also raised a complaint and requested my days salary be reimbursed for waiting for the engineer. I need to send the equipment back (less than £100) when I receive the box. Today I have received notice I’m being charged £403 on 2nd May. That’s £17.49 of if that is charges for usage. I didn’t have usage, only error messages and was written to to say that they’d received my 30 days notice of my intention to leave and reconnect to Sky 16/4/25. Sky connected me sooner so I switched off Virgin on 12/4/25. Please can you look into this. There should be no charge at all as I never had connection and you failed to install correctly which is why I left after the engineer didn’t show….. when I receive the boxes I will return your equipment. Even with a 30 days notice notice at a monthly  £34.99 a month where does £402 come from? There clearly is a big error here …..