Discovery Lying about 55days Interest Free Credit Card

Hi,

Trust you are well.

I am getting charged interest on my discovery credit card every month, despite settling the full outstanding balance every month. When I start the month, I start with R0 owing, at the end if the month after all my swipes, if I owe R10 000, I pay the R10 000 in full. My understanding is that is it 55 days interest free.

Why am I getting charged the interest every month? I tried calling in to log a complaint, waited 15mins with no answer.