Cashu isn't a company that controls the ecash. It's the protocol. The cashu mint you SENT from controls certain aspects of the tokens and the collateral backing them, but that comoany even does not know where you sent the token.
What you generated was not an invoice, it was a cashu token in QR code form. If your wallet saved a copy of it for reference, then you still have it, and there should be some way to scan it back into that wallet or any other wallet that's connected to the same mint.
I have a similar problem, and have not yet attempted to fix it because I couldn't be bothered lol! You fix it by finding a copy of the token wherever you might find one (maybe there is an option on that payment to reclaim the token?), storing it on a cashu wallet and then swapping it so that it's no longer "pending."