I have an order for ghostwriting and the seller had already sent me the initial files for review, I saw some things with my order that were needed to be modified and she already agreed on the revisions and will be working on them.
However, upon checking my phone in the morning, Fiverr notified me that they cancelled my order, refunded my money, and I was also no longer able to contact the seller. What should I do with this and why did this happen?
You will need to ask customer support why it happened.
Okay noted.
No, I did not request for an extra payment because he/she included ‘unlimited revisions’ in the offer. Also, we already agreed on the revisions, and delivery time of the revised files. I have sent a modification notif to her as well.
It’s unusual but customer support is the only place you can get the reason it happened.
I have already contacted customer support for the issue.
My concern now is whether I should wait for the answer of customer support or should I just get a new seller. As, of course I have already lost a lot of time.
I think it is a good idea to look for another seller. You’d mentioned that you were no longer able to contact your seller. I don’t think that would change in the future. It could be that your seller either:
deleted their Fiverr account, or
got their account deleted due to a ToS violation.
Are you still able to see your seller’s profile?
However, you will have to wait for CS’s reply (can take up to 48 hours) to get a definitive answer.
But, in the meanwhile, I think you can already start looking for other sellers.
Good luck! 
Yes, I guess that would be the most practical thing to do.
Yes I can see his/her account but I cannot contact them any more.
In that case, it could also be possible that the seller blocked you (by mistake? IDK). If/when a seller blocks a buyer, the buyer can no longer contact the seller. Is it possible that the seller also canceled the order? 
This seems very strange considering you’d mentioned that the seller already agreed to the revision request and had also given you a specific delivery time for the revised files. This is the reason why I didn’t mention the possibility of a block (from the seller) in my previous reply.
I don’t really know because this is my first time buying on Fiverr.
However, the email I got from Fiverr said that
“We had to cancel your order with (seller username), as they are no longer available on the marketplace. Keeping our community safe and secure is a big deal for us, and we want to make sure you get the highest quality of delivery and service.”
Hmm… this probably means that they’ve been suspended from Fiverr or something. In any case, I think you’re better off finding another seller who is capable of completing your project. I hope you have better luck with your next seller. 
Good luck!
Yeah, I really shouldn’t be wasting any more time.
Thanks for your help!