I ended a contract because I felt I didn't understand the requirements and it was difficult to get in touch with the client. However, I've since figured out how to complete the assignments, and since I am still getting emails from the client notifying me that I have work available, can I re-open the contract?
Nobody can re-open closed contracts.
Clients are able to create new contracts from scratch OR create new contracts or job postings based on previous ones.
Don't do any new work without a contract open and active. You won't be paid if you work without an active contract.