I have the same problem with my BLU Vivo XL after about 8 months. I can get it to charge only after several minutes of jiggling the USB connector to get the right connection. The USB data connection is also broken so that my car does not recognize that the phone is connected so that Android Auto won't work - nor can I transfer files/photos/music between phone and PC.
I had a similar USB issue with a JBL Flip 3 speaker where it could not be charged. JBL sent me a replacement speaker free of charge without even waiting for me to return the defective unit.
BLU should just own up to this issue and replace these phones!