Bad Service

I have had my RCS account for over 5 years . No problems until this year .Bad Service call centre rude . For the past 3 months i paid my RCS account via my app . For April i could not pay via the app. When i called the call centre i was told they cannot deal with me because my cell phone number was different and my app was blocked. So i went and paid my account on the 4th May 22 at Foschini Centurion Today i got a letter that i am in collections because i have not paid. I paid the amount as per the April statement. The letter states i have not paid for this month i have not even got this months statement. I got the same reception from the call centre cannot deal with me . Now my account is in ***** department. Please RCS explain to me what is happening . Also i have the same cell phone number for the past 18 years . It is the same one RCS communicated with me all the time