I am sorry to tell you that you have raspberry root rot. It is the most common killer of our raspberries. It is a soil borne fungus and can spread in soil water or root to root between plants. The typical symptoms are decline and death of the bearing canes while the new canes usually look great. This can go on for quite a while with your not getting a crop. Raspberries require very good drainage at all times. The organism was probably in the soil and when you transplant the open roots are very susceptible. There is no cure. If you have bearing canes away from the sick ones, you can try to transplant those to a raised bed, but chances are you will simply spread the disease. Better to just start all over in a new site. There has been some research that amending the soil well with well-made compost can help for the new site.

Thanks so much. So we should start,over with new plants and a different site as well? such as a raised bed where we have brought in different soil?

Yes, I am afraid that is the best answer. I had to completely replace 60' of raspberries because of the same problem and the new bed is now almost 10 years old and doing well.

Can I plant other plants in the same area? Such as flowers,etc.

Yes. Almost any flowers are fine. Avoid small fruits of all kinds. Cabbage family, most greens, no problem. Tomato family just a touch iffy, but not bad as they are raised as annuals here and the pathogens can't get the long start they need.