Well, for once, we at TransferXL are, maybe counterintuitively, happy that we cannot help. Let us explain.
For the best possible encryption, we do not use so-called server-side encryption like most solutions. If this were the case then, of course, our servers would necessarily have to know the password in order to do the encryption. And once the servers have access to the password it is a small step to store it.
However TransferXL works differently. TransferXL uses client-side encryption whereby the files to be transferred are encrypted locally on the computer or device that is doing the upload. In designing our security approach this way, our servers do not have access to the password at any time. This guarantees that we cannot hand out your password to anybody else but, unfortunately in this case, that also includes you.
So even while the encrypted transfer may still be available for download we cannot help you with decrypting the transfer in case you have lost the password.
So please be careful in safeguarding your password, note that there are many solutions out there that can manage passwords so we would advise you to look that.