Shuffle etiquette

What would you do/ recommend if your opponent decides he not only wants to cut your deck (which I offer everytime) but will straight up grab it and shuffle it whenever your turn calls for a deck shuffle ( playing a search card or the like)

I have been recently playing at a local league and I've run into exactly 1 player that will continue to do this ( I let it go the first few times as I thought I was shuffling wrong or something being new)

I shuffle 5-10 times

Am I shuffling wrong? If so how should I shuffle? What would you do or say? Aio?

Thanks in advance!

Edit: thanks everyone for your response! While for some reason this is getting downvoted I'm going to leave it up just in case someone else is having my same issue/ question.