Ask HN:Someone mis-using company name and charging non-customers

We are early stage company with recurring online subscription.

Recently few unknown individuals(not our users) contacted us asking us to refund the amount and claiming that they have not heard about our service before.

Turns out that there is some 'unknown' entity/person with similar name who have somehow acquired card info of these persons(not our customers) and making it look like its our startup.

No one picks up the phone number given in the credit card statement these individuals are sharing, and there is no data i can find if I am doing paid phone look up.

So far I am asking these individuals to file dispute, but I am concerns that its hurting our credibility.

Any thoughts on what can be done?