cannot change custom login logo

I have a woocommerce wordpress site that i duplicated. The original had a custom logo at the login page. After I duplicated it I could not change the logo. Also, i noticed that the plug-in did not carry over that allows setting a custom logo. In fact, when I went back to the original, the plug-in was missing from there too. I never disabled or deleted it though. Now, even when i reinstall the plug-in, (custom login ver. 2.1.9), it doesn’t work. Its as if I cannot over-ride something. I even tried a different plug-in, (Webriti Custom Login ver. 0.1), still cannot change it. I eventually deleted the logo from my media folder, but now there isn’t a logo at all, not even the WP or woo logo. Has anybody had this problem before? How can I resolve this issue without rebuilding the site from scratch?