Settlement Query

Asked for settlement quote on 2 accounts and did 1 payment on both, sent proof with combined amounts, they decided to split the 1 amount on 2 accounts which left me with arrears on 2nd account, sent emails no response, after realising that i still have arrears, my problem is the proof of payment is 2.1k but you decide to use only 1.3k what happened to the balance as i am in arrears