Yep, same here. I live in PO4. Broadband was not too bad in the evenings because I was regularly checking the speed just before signing a new contract. This week it's so bad that it started dropping out entirely — it's like someone flipped a switch and we become the latest postcode to suffer. There's no way I can wait until May for a "review" (that's not a fix by the way) because my eldest daughter is currently studying for her GCSEs and needs a stable internet connection to access online coursework/revision notes. I'm going to cancel my contract if it's going to take until May to just to "review" it because that's totally unacceptable.
The problem is clearly that VM are taking on too many customers when they are unable to provide the service due to lack of capacity. Once VM run out of capacity they should stop selling into an area and wait until they've "fixed" the problem. Unfortunately, what they do is pile on more customers and make lots of promises about "review" dates and "fixes" that keep on getting pushed back.
I had exactly the same problem with VM just over 2 years ago and it took 8 months to be fixed .
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"Cable broadband is typically faster than copper-based services, but a significant minority of users experience severe slowdowns in peak times." — Ofcom, UK Home Broadband Performance, November 2016