If it isn't what you wanted the simplest solution is to return it.
There will be nothing you can do if there are hardware differences between the dual-SIM and single-SIM models. And it would be absurd if there weren't hardware differences: if they are the same hardware then what would be the point of adding to their costs by writing and maintaining a second firmware build which disabled some functions (plus all the overheads of managing, markering and distributing a second model), and then presumably selling it at a slightly lower price as it has less functionality? That would be a crazy thing to do.