Are you saying that you are a buyer and definitely not a seller? If you have ever had an account which offers services for sale on Fiverr, they may think that you are operating multiple accounts or doing something untoward. I don’t believe that anyone should be banned without being given the opportunity to forward their side of the story. However, that’s the way Fiverr seems to roll.
Usually, when sellers are banned, they have to guess why and hope that Fiverr will release any cleared funds after 90-days. If you are a buyer (exclusively) I imagine that you would have more options.
If I were you, I’d send an email to Fiverr stating your case, before notifying them that they have until X-date to reply. If after this period Fiverr still doesn’t respond, you can then send a copy of this email to PayPal and/or your credit card company.
As long as you make sure to date everything and document all communication, this should result in PayPal or your credit card provider intervening on your behalf.