Yes there is such a law, it is called defamation. Whilst this may indeed appear to be a potential case of defamation (this includes libel if it is in written form, or slander if it is in oral form), such claims are extremely difficult to pursue. Many people are intent on suing for defamation without having any appreciation of the law behind them, so I will try and clear things up for you now.
First of all, certain conditions must be met for the statement to be classified as defamatory. These are:
1. The statement has to be untrue.
2. It must directly identify the complainant.
3. It must have been published, usually communicated to at least another person.
4. It must be in a form of words, which would tend to lower the claimant in the estimation of ‘right thinking members of society generally', expose the claimant to hatred, contempt or ridicule, or cause the claimant to be shunned or avoided.
5. Its publication has caused or is likely to cause serious harm to the reputation of the claimant.
Whilst it may be easy to prove that defamation has occurred, the legal process of pursuing such a claim is extremely complex and expensive. As this goes through the High Court, you would need the professional help of specialist defamation solicitors and the costs are undoubtedly going to run into the thousands right at the outset. Also there is no legal aid available for such claims so the complainant must fund these personally. So when you hear about defamation claims being made, these are usually pursued by big corporations or celebrities who have a public image to protect.
You must also consider whether the party alleged of making the defamatory statement can defend the claim. Even if you satisfy the criteria to prove the statement was defamatory it could be defended on a number of grounds, including by providing evidence that the statement was substantially true or an honest opinion.
There is of course nothing stopping you from contacting the other party and threatening them that what they have done amounts to defamation and that you will consider pursuing the matter further if they do not retract their statement. This could prompt them to reconsider their position, but I would not recommend that you actually proceed with a claim for defamation due to the issues highlighted above.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating (3, 4 or 5 stars) as that is an important part of our process and recognises the time I have spent assisting you. If you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you