Bill is wrong

I need help please. I recently changed contract and was given a summary of my next 2 bill payments before my new contact starts at the agreed rate. My first bill is completely different to what was agreed and try as I might, Chatbot was useless and telephone bot seems to deliberately misunderstand, offer an option for a new direct debit and hangs up. I registered a complaint which was acknowledged after submitting but then nothing! I feel virgin are making simple errors hell to resolve and it must cost a fortune in productivity.