Dstv to be open cos I have paid them

I have paid R675 on23rd December 2020 and my account was open the dstv was on and on the 1st of January my account was closed again when I called the told me that I have arrears that I don't know. I was my dstv account to be open cos since that time its been closed. My kids are family it's affected by all these. I want to know why it must closed and I wast it to be open with no cost because I have already paid it. Why must I pay R420 now as they are suppose to open my account