I have created an open-source project in github and R around financial calculations under GPL v3.
Today I saw in the traffic graph of github that someone cloned the repository and that there was a visit from this referring site: jira."company name".com
I researched a bit the "company name" and it seems that it is a financial technology company which sells non open-source systems.
So, it is apparent that they downloaded my software and even put a link to their jira system towards it.
I think that this is illegal, correct? How should I proceed so as to ask for a fee for the use of my software?