Annoyed

My last purchase and payment on my Foshini account was in 2018. Since then, I've been receiving monthly sms's to inform me that my installment for the month was R0. I found this monthly sms to be useless actually. Last month though, my sms read that I owed R348 and that my installment was R49! I never bought anything on account or cash from Foshini since 2018! I went to the store and asked for an explaination. I was informed that it was account benefits that have accumulated since 2018. Why have I been receiving sms's that say I owe nothing for years and then suddenly R348?