Poor service - Policy Canceled but I am still being debited

I have taken up the "First Warranty" plan with FNB and canceled it during the cooling-off period due to taking a Warranty plan from another provider. I was assured that I will not be debited. On 02.09.2019 I was debited. I attempted to call the number provided on the website *** however I was on hold for over 20 minutes so I reversed the transaction on my banking app. On 01.10.2019 I was debited again and again tried to call the number provided on the website however I was on hold for a long period again. I now can not reverse the transaction myself as it is over the limit for self service. This is frustrating and puts me out of pocket. Why are companies so quick to answer the phones for new business but can not answer the phones for a query? Also why can a simple instruction not be completed? I want my money back!