[PubQ] No response to submission withdrawal request?

Last spring, I sent an R&R to an agent who had requested it. I received no response after confirmation of receipt and have shelved the manuscript, written a new one, and am getting my query life together.

The agency has a no-simultaneous submissions rule. I reached out the the agency inbox asking to withdraw the submission so I could query a different agent whose MSWL better fits this book. I haven't received any response after a week and a half. At what point should I send the new query along to the new agent?

Thanks for your help!