arrears are high.

on 6 November 2015 bought a bed on credit which was R3999.99,paid deposit R400 not their 10%,13 November 2015 paid R3999.99 balance was R1756,on the 21 December 2015 I paid R1922 which was the new balance. What is the legality for this arrears occurred? If this Is not fixed, Lewis store bye.