Thank you very much for clarifying. First of all, I am sorry to hear about the issues you have experienced in your situation.
As you have correctly identified, this will not be a case of defamation as the comments are true and they must have been false for them to be defamatory. Therefore, harassment may indeed be the most appropriate option here, considering there are no legitimate purposes for which these comments are continuously being made still.
Such conduct could likely amount to harassment, which can be either a civil or a criminal offence. The Protection from Harassment Act 1997 states that a person must not pursue a course of conduct, which amounts to harassment of another and which he or she knows or ought to know amounts to harassment. Although there is no definition of what harassment is, it would usually include alarming a person or causing them distress and must have occurred on at least two occasions. It could be verbal or physical acts, or both.
How this matter is dealt with would depend on whether the victim wants to take it down the civil route or the criminal one, or even both.
The civil law route will have to be pursued through the Civil courts and must be initiated within 6 years of the alleged act(s) of harassment taking place. The court can make an injunctive order instructing the harasser to stop their behaviour or place certain restrictions on them. For example, it can forbid the harasser from doing certain things such as being physically violent, contacting the victim directly or indirectly (by making someone else contact them), or going to their home address or place of work. If the victim is related to the harasser, then it would be dealt with via a non-molestation order, which has similar effects.
To apply for an injunction, application form N16A must be completed, available here: https://www.gov.uk/government/publications/form-n16a-application-for-injunction-general-form
If they still do not stop harassing the victim, it would become a criminal offence and they can be prosecuted in the criminal courts. It is also possible to seek financial compensation if financial or emotional losses have been suffered (e.g. causing severe anxiety or distress).
To apply for financial compensation, application form N1 must be completed, available here: https://www.gov.uk/government/publications/form-n1-claim-form-cpr-part-7
If the matter is reported to the police instead and they take it further and prosecute, the punishment for harassment can be imprisonment and/or a fine. A court may also impose a restraining order for the purpose of protecting the victim.
Before the courts or the police get involved it may be better to try and resolve this directly with the harasser. They should be warned that their actions are being treated as harassment under the Protection from Harassment Act 1997 and that unless they stop what they are doing they will be reported to the police and legal action under harassment legislation will be taken against them. If that does not help, the matter can be taken further either by contacting the police and letting them deal with it as they see fit, or starting civil court action as described above.
Finally, here is a very useful and detailed resource about harassment in general: https://rightsofwomen.org.uk/get-information/violence-against-women-and-international-law/harassment-and-the-law/#What%20is%20harassment
Hopefully, I have answered your query in a way that is simple and easy to understand. If anything remains unclear, I will be more than happy to clarify it for you. In the meantime, thank you once again for using our services.