If someone is posting false information about you on social media it can be a criminal offence depending on the exact nature of the information and how they have posted it.
For harassment to be committed there must be a ‘course of conduct’ (two or more related occurrences). The information does not necessarily have to be violent in nature, but must be oppressive and need to have caused some alarm or distress.
If the information is indecent, grossly offensive, obscene or threatening/menacing, then an offence relating to ‘malicious communications’ may have been committed. This offence does not require more than one incident.
You should report this to us via 101.