Check every statement in detail...they are *****ing from you!!!!

This is a warning to everyone. Check your statements.Always expected the company to be honest. Until I checked my statement. They still charged me interest for a purchase I made 7 years ago.They told me it was because my account never was paid up...so I send them my statement that I was actually in credit 2 years back...yet they still charge me interest for a purchase i made 7 years ago...I queried it...and i was told the the statement and the interest is correct. So i asked that they explain it to me that hownis it possible that I'm being charged interest for something i already paid...Once again the response was that everything is okay...and the the sound of silence when i send them the statement where i was in credit...been waiting for ansers for more than a week...i asked multiple time...that i want answers...Nothing...so lets see if i get a response now...i don't want calls.. i want emails so i can paper trail