Hello Samuel,
Release the OLD design if it covers the client's requirement no matter how ugly it is.
Being 4 weeks late with no NEW design ready is a significant failure on the Managers part and I think there is a crack in your communication line with the Upper management and the client.
The client should've been notified 5 weeks ago that you need an extension to deliver the BEST design and the management should have put pressure on you to deliver within the agreed time frame.
Set delivery dates that are realistic and strive to achieve them and ALWAYS keep your client abreast of the development, that ensures trust is kept.
#Peace ✌