Claim stale but submitted on time!!!!

So we submitted a claim to the scheme within in the turn around time of 4months. We had no success with this account until date, when the accounts lady called TODAY she was informed that the account is stale. 1. Call ref 090518QSPS4 - To submit the account Emailed the account REF100518QS66LZ 2. 220518QSRM8L - Followed up with 3. 060618QTJ3D0 4.150618QTZJ14 5.230718QXR3XK - Spoke to Nevel and asked to speak to their teamleader as feedback was not recieved. The teamleader Verona does not want to speak to us but will send the claim for reprocessing 6.270718QXZLD9 - Niven - claim is processed but it is stale!!!!!!!! Why was this account not processed on 10/05/2018 when we submitted it to the scheme. Who do we keep liable for this???????? No answers as the teamleader doesn't want to speak to us but yet they take our number to contact us.