CTC in payment but CoL payment refused

cl has been in receipt of CTC for over 10 years and during 2022/23 their entitlement was circ £24/wk.
Cl received a renewal notification in Sept asking for confirmation that their 16 YO son would be continuing with further ed. Whilst the cl was providing evidence to support the CTC was suspended for 3 weeks and then when evidence of the continuing education was received, cl received a back payment i.e. CTC was effectively in continuous payment.
Cl received the first CoL payment in 2022 but not the second one worth £324.
Call was made to HMRC and initially cl was told they were not in receipt of CTC during the qualifying period for CoL payment. During a second call made to HMRC cl was told their income was too high to receive CoL payment, a third call was made, pointing out that CTC was in continuous payment over the last 10 years and that, based on current income, cl is still eligible to receive CTC but call handler insisted income was too high, without providing any detail ( call handler subsequently hung up)
Cl has not received the latest CoL payment for 2023 either.
Has anyone else had this issue. Will be rising a MR and a complaint but interested to know whether there is an underlying issue with HMRC systems?
Thanks for any thoughts you would like to share