Misinformed about payments and penalties

I took out a two year contract for LTE, and my my monthly charge was R274.60. I never skipped a payment. In December 2019, I went into the Telkom store to inform them that something was wrong with my bank account, and asked where I could go and pay that money. Bear in mind my payment was to be debited from my account on the 5th of January. I was told that I could make payment at the post office, which I did on 31 December. When I received my February bill, I saw that I was charged R202 for rejected payment. I was not informed that I would be penalised if the money was not in my account. I have never skipped a payment in the two years of being a loyal customer, and even paid the money 5 days before it was due. Now I must pay almost double for my contract, and it expires on 5 March. I am so disgusted by their service. I am very upset, as I went in store first to query, before I made any payment. The lady could've advised me of the penalties. I am so angry.