Sue the anonymous person who stole your account and sold it to someone else, who is probably nowhere near your jurisdiction? Good luck.
Suppose Mallory finds the contact information for Alice, an Instagram employee working overseas. Alice is paid next-to-nothing and wouldn't mind Mallory's extra cash. Mallory posts to their Telegram channel: "Instagram account takeovers for sale! Pay me $5,000+ and I'll take over ANY Instagram account". Mallory gets buyers lined up and promises to take over the accounts when Alice is working. The next day, when Alice signs on to the administrator tools, she sets each account's email address to the ones specified by Mallory, and Mallory pays her a percentage of what she charged. Mallory and Alice continue their scheme for about a week, when Meta finally investigates the situation, traces it to Alice's user account, bans or reverts every account Alice helped steal, and terminates her employment. However, no legal action takes place against Alice. Why? That part, I'm not so sure about. They're able to trace every action to Alice, and Alice is not anonymous, thus they have every ability to bring a case against her. Once Alice's employment is terminated, Mallory simply finds another employee willing to do their bidding. New hiring waves make this easy.
I'm happy to go into more detail about the underground Instagram account market. It's fascinating: people bragging about bribing employees and taking advantage of them, knowing their employment will be terminated, and actively showing off how much money they make. Meta has tried in the past to hit certain high-profile people with a cease & desist letter, but those are hard to enforce in certain jurisdictions.
When they want to. Not when YOU want them to.
Arbitration clauses are very strong in the United States and have been getting stronger for years. Across both Democratic and Republican administrations, in state and federal courts, judges constantly reaffirm that these provisions are binding. Even literal shrinkwrap arbitration clauses on foods (Vital Proteins, Daily Harvest), etc. are upheld.
Exceptions are rare, such as unborn babies getting sick who never signed a clause such as with Daily Harvest, or when a case is public enough to draw backlash such as with the Disney+ trial arbitration clause being used to prevent a man whose wife died at a DisneyWorld restaurant from suing. Even parents suing on behalf of their pre-teenage children (e.g. against Snapchat in an Illinois court) find themselves blocked by arbitration.
There is no way merely having someones Instagram hacked and having "their username stolen" (not something possible, it's Meta's property) will make for such a rare scneario.
Per Instagram's ToS, if you sued instead of filing a Notice of Dispute (i.e. arbitration), you would be forfeiting the provision where Meta pays for your arbitration and other fees for claims less than $75,000. You would also be risking a decision from the arbitrator (AAA, who you should expect to be biased to favor Meta) that you would also need to pay Meta's legal fees.
If you try to sue, your lawyer will tell you all this.
Not expecting to win a dime from Meta, your lawyer would only represent you if you have pockets deep enough to fight a losing fight.
Then you will be competing in an American Arbitration Asssociation's 'Alternative Dispute Resolution', which is even less favorable for the consumer :D