Welcome to the mineral rights forum.
If you haven’t already, send them a certified return receipt letter with your request. Not sure how long you’ve been waiting, but expect more than a month most likely.
Also, you don’t mention what is in your package - but my experience is that companies want probate in the state in question. Some companies may accept an affidavit of heirship; but it depends on how much risk the company is willing to take.