Application to extend 10 year route invalid due to non payment of health surcharge

Hope someone can help!

My cousin was granted the 10 year visa route in 2013. He successfully applied for an extension after 2.5 years in February 16.

Another application was submitted to extend for further 2.5 years, before the visa expired expiry in November 2018. Even though the fee waiver was rejected, we subsequently paid the application fee (Feb 19)and completed the bio-metrics (March 19) as soon as they were requested by the Home Office which was communicated by a posted letter. He did not receive any letter regarding the Health Surcharge fee otherwise this would have been actioned immediately.

However, as a result of non payment of IHS, the Home office have rejected his application claiming it invalid due to non payment of the IHS which he never received notification about.

We have written a letter to Home office stating we never received any Immigration Health Surcharge notice and asked to reconsider his application as the refusal letter gives no option for admin review or appeal but just says he needs to return to his original country!

Someone has advised to make another application within 14 days but again, this is not mentioned in the refusal letter!

Does anyone know the rules around this and section 3C?

Except child application every adult pays IHS at the time of submitting the application otherwise the application is deemed invalid. In my view even the application is submitted in timely (before visa expiry) but if was invalid then section 3C wont come into play.

Yes,but the Home Office are supposed to give one opportunity to rectify any missed payments. As per my initial post, no attempt was made so where does this leave us?