unpaid claim

I've been a member of NHB sadtu funeral policy for more than 3 years. My monthly payments are always paid via debit order,I made a claim last week when one of my dependent passed on. My claim was declined and the excuse they gave me is because my August premium was unpaid. I wasn't aware of this, they never informed me about it until last week when I made a claim and they were supposed to pay me. What is confusing is that my bank statement indicate that the debit went through,the money was paid to them. According to them I missed one payment, I even went to the extent of requesting them to deduct that monthly premium in the sum that they were supposed to pay for the claim but they declined that request. I can't believe they did this to me after more than 3 years I've been a very loyal client to them