My design stolen from the author ThemeForest

My copyrights have been violated by one of the authors Themeforest [REMOVED]

I have not gone though details, but you can send DMCA notice to author via envato support team.
Make sure to provide full details and DMCA notice is in valid format

I don’t think posting here is going to help as it is a copyrights discussion and would be locked eventually. You should contact Envato Support and also send in a DMCA. If Envato receives a DMCA, they would take down your copyrighted content.

Contact suppor, i guess it should be hard to say IF you two would not have been contacted previously, he could said that took some inspiration from your work. But I must admit that seems pretty suspicious.
Contact support and send the DMCA.

The other replies are correct. If you feel this is the case please submit a ticket here but please do not discuss copyright issues in the forums as per community guidelines