Sure you've probably already gotten past this issue. But just in case.
Please keep in mind that most cages are suppose to be used while you're completely soft. Snug but not tight to allow for proper circulation. But if you're having that much of an issue it could be a number of things. If you dont mind sharing some measurements I'll see what I can do to figure out the problem.
Could be the device is to small, could be that you're not fully soft, could be something as simple as not knowing the stocking method (quintessential tip for newbies of chastity). But if it turns out that its actually just coming down to you being 'too big" i'll see if I can find a more appropriate cage.