I trust that you have reported this to the police and you have an incident number. If not, you need to do it and get it and give the incident number to the phone providers and tell them that if they pursue this, you will defend the action and you will ask costs to be awarded against them on the basis of their vexatious and unreasonable behaviour.
You might want also make a complaint to Ofcom about their aggressive tactics.
Tell them they are now harassing you and they are in breach of section 40 of the Administration of Justice Act and the Protection from Harassment Act and you reserve the right to apply to court for an injunction to stop them writing to you again and you reserve the right to ask the court to award all those costs against them.
Tell them that they should not write to you again but they should issue court proceedings which you will defend.
Can I clarify anything else for you?
I am happy to answer any specific points arising from this.
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