Click & Drop

Cannot send orders to the USA any more, as keeps saying "Duty amount cannot be zero". I am using the MPR option and It was absolutely fine until Monday 24th November and then this issue started. I have contacted the help team and technical department and no one has helped me at all. I have sent screenshots of issues and got no reply. At present I am having to send all parcels manually through send.royalmail.com, which is far from convenient when I have to enter all details manually. I have tried clearing my cache, using a different browser and deleting the app, but so far nothing has worked. Works fine for all other countries