Unable to back up my phone

I was having trouble backing up my iphone on my Mac and PC. My iphone has 64 GB and I haved used 63.5 GB. As I tried to back up on my Mac, which has about 100 GB, the not enough space popped up. So I switched to my PC which has about 600 GB of free space. But I am still getting the same message. I have tried to contact apple support, restarting both of my devices did not work at all. So I cannot back up my data at all now.