Discovery bank - Pathetic service !!!!!!!

I've had a discovery credit card for years and I settle the full amount every month to avoid being charged interest when querying why I was charged interest on my February statement despite settling the amount owing on the Jan statement by the 9th of January the consultant could not explain , all she said it's based on the money used , I tried with great frustration to explain how I managed the account even told her to look at previous months accounts , she again could not explain , I was then put on hold while she investigated where she assured me it would be no longer than 2-4 minutes.. so much for skilled consultants. An utter waste of 30 minutes of my time