Eddie vs Grundy national bank

i have been in many business for several years i used (GNB) for a lot of my banking and i use several other banks we would ask (GNB) for and interest payment we didn"t understand what they where doing for many years they where taking the interest from that month adding it to the next month and i was paying 5% of the total loan as a penalty for that month the contract does not say this at all we thought we where getting and interest payment no other bank that i deal with does this. Note: i have spoken to several other people that had been done the same way. This could go to Federal case i live in Kentucky and the bank is in Virginia