This is service work, this isn't Walmart. You can't get a refund, the best you can do is end contracts as soon as possible. Hiring software contract work is always, always risky for startups. This is why. Quality varies highly and it's expensive if you choose the wrong person.

Worse is that you did a 'chargeback' on paypal which is a dirty tactic. Considering how awful Paypal's dispute process can be.