Are you prepared to bear the cost?
It is never really that simple.
The only way to force the information is to seek an injunction from the civil courts. That is easy enough in legal theory. It is a matter of showing that you have an argument that is valid that you cannot bring without this information. Usually data controllers are perfectly happy to hand it over when there is a court order as then there is no allegation of breach on their part.
The problem is that even if you get the anonymous call it wouldn't normally identify the caller unless you were able to recognise the voice. It might be all an expensive action to achieve nothing.
But if you are intent then you need to seek an injunction from the county court. It will cost about £350-£500 if you appear unrepresented.
Can I clarify anything for you?
Yes, but you have to prove it was that person.
You can use the N20
Sorry for the delay.
Not for an injunction.