Thanks, that is a standard letter fro them. It's a small claim so they will not go to the expense of using debt collectors nor suing you yet.
If the service was poor then you can allege breach of contract against Vodafone (breach of your consumer rights and breach of the Consumer Rights Act 2015).
First of all make a formal complaint against Vodafone and if that does not resolve the matter ask them for a final response letter (a "deadlock" letter). You can make the complaint with Vodafone here: -
Once you have the deadlock letter the next step would be to escalate this to the adjudication scheme (CISAS) - they will investigate and liaise with Vodafone which would hopefully result in a refund of any monies paid and a cancellation of their bill. They can also order the internet company to make a financial award if they have acted badly.
The service is covered by the Consumer Rights Act 2015 so you have a right to expect a reasonable service - if they do not provide that then the regulator will step in but it also means you can sue for any damages or losses incurred as a result of Vodafone's conduct.
You can escalate to the adjudicator here : https://www.cedr.com/consumer/cisas
If you have lost any money then you could sue Vodafone but the court may consider that to be premature if you do not go through CISAS first of all.
You can sue for your losses via the http://www.moneyclaim.gov.uk website which is easy to use and no lawyer would be required.
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