I HAD the exact same problem. I did some research, tried a whole bunch of different stuff and even considered buying a new battery (since I too have left my phone charging overnight on many occasions), and if that didn't work, I would replace the USB port.
But first, I decided to simply CLEAN the USB port. I removed the battery, then I used a plastic dental pic to pluck out any dirt and debris. Then I folded the corner of a paper towel into a sharp point, dipped it in alcohol and rubbed it all around inside the port to remove any oxidation on the internal prongs and central metal tab. Next, because plastic isn't strong enough, I used a METAL dental pick (again, dipped in alcohol) and very, very slightly BENT the metal tab more to the " inside center" of the port by sort of rocking it back and forth, again, very slightly. You definitely do NOT want to BREAK it! Lastly, I replaced the battery, plugged it in and VOILA! It began taking a charge! I charged it to 99% and unplugged it. That was yesterday. This morning, with the phone at 35% , I plugged it in to top it off, but AGAIN it would NOT take a charge. So, I repeated the tab bending process from yesterday and it is NOW CHARGING AGAIN.
The bottom line, it seems to me, that BLU phones have a really cheap and crappy USB charging port, that's all.
I suggest: 1) Never over-charge your battery. 2) Download a Battery Charge Notification app.
If you don't happen to have a metal dental pic, I suppose you could use a thin metal nail file, or perhaps very thin tweezers. Hope this helps all who suffer this cell phone nightmare. (excuse the hyperbole).