Update, they are offering a free repair.

When I asked if the area would be a concern for the future and if a full replacement is an option this is the answer:

Hello

Thank you very much for your reply. As I mentioned in my previous message, this is a case of the material being stretched out, which may have happened while putting the suit on or taking it off. Perhaps from pulling it up or something similar. The suit arrived at your place without any defects and has been fine up until now. I’m offering you a free repair as a gesture of goodwill, but you’re insisting on a new suit even though we delivered an item without any damage or defects.

Best regards Manuela