Charged an extra £17 for imaginary changes to my package

I'm on the M125 broadband and I have a discount because there's no way I'll be paying "full price" for this service. I am normally charged £51 and have a £25 discount so pay £26 a month. On my latest bill it wants to charge me £43 and the reason given is that apparently some changes were made to my account on the 17th.

There's no way I've made any changes to my account when I haven't even logged in or had any contact with Virgin Media, so it seems they're just making it up as they go along. The bill is just a complete mess and I can't make any sense of it. It lists a "price rise charge" which I read is something like RPI plus a few percent, so no way it should come to £17 more a month. My discount is applied til next year so it's not the discount running out.

Does anyone know why Virgin Media are doing this? I've had terrible connection problems for the past few months that haven't been resolved despite emails from virgin telling me they're aware of the problem, and now I get these extra charges to add insult to injury. I really don't want to have to call the Indian call centre but I am afraid I might not have much choice.