Bogus Powerbanks

I ordered 2 powerbank said to be 20000mAh and upon receipt we fully charged them before using them. On the package it is written 30000mAh. When we used to charge our cellphones, it only charged my cellphones from 15% to 65% and it went off, the battery was drained. Same for my husband. We charged them again and this time they only charged the phones each at about 50% and the battery went off. So you sold us lies here