PLANET 54 RENTAL SETTLEMENT( WRONGFUL ALLOCATED ARREAS)

I am writing for the second time here about the same issue with planet 54, i am very frustrated and regretting to involve myself with this company as the do not have best interests to their consumers, i have had a rental contract with them cancelled it and duly paid whatever that i owed as per the agreement. they sent me a paid up letter. to my surprise it appears that i still owe them monies and i am in arrears, this affecting my credit rating i am trying to buy a car and this is blocking me. i have emailed them last year and they promised to sort it out but until today it is not sorted out. they are now not responding to my emails.