Is you ServiceProvider an heavyweight object? Does it have state? If no, then it's not flyweight. Also, it's not really a flyweight object unless you are sharing Service provider among multiple instances of MigAccount.
Also, an important thing to note is that not all cases of multiple objects sharing the same object is an example of the flyweight pattern. Ther3e are a lot of patterns that are based on multiple objects dependent on a single object. What matters is not that they are sharing the object, but why they are sharing the object. What you have described here looks more or less like a service injected into a client. Nothing here tells me that it's a flyweight pattern
It's a flyweight pattern only when the shared object (or pool of objects) stores the state and they are immutable. When the state changes, instead of creating an object every time the state of the object changes, you get a object from the pool that represent the new state.