"There is no way to adapt it."
Actually there is....
"All lenses from SIGMA's new three product lines (Contemporary, Art, Sports) will qualify for this paid “Mount Conversion Service”. It enables customers to convert the mount of their current lenses, and we will change the relevant parts for a different mount and its internal core system accordingly."
Sigma has offered this service for some time now. However, I hope the OP knows or realizes this is not a free service. The OP is far better off to return the lens and buy the correct one. Plus the OP needs to find a more honest or at least knowledgeable dealer.