Access instagram linked to Facebook

I have an old instagram account linked to a commercial (artistic) profile. It turns out that for some unknown reason, even though he knows his instagram login and password, he insists on sending a code to a cell phone number that I no longer have. As I don’t have access to Instagram. I try to get in but he insists on sending by the number.

I try to get on facebook, but it gets on my personal instagram not on my page. How to solve this.