disgusted

on the 11 January 2019 bought a few items on my account I bought a pair of nike slides size on the 11 January 2019 on the 14th January I returned it again for a bigger size then the lady at totalsports told me I cannot buy as my account was suspended that was fine cause we are 1 month behind with payment I returned the slides cause I could not take a bigger size she credited the R359 back to my account fine .on the 28 January 2019 I made a payment of R500.00 to our account then it said that I could still b ye for R646.00 on the 12 February 2019 I wanted to purchase 2 items online and then it said I have a nil balance how is that possible cause there was R646 credit available and we bought nothing I would like to know as to why in the first place they gave us credit of R646 and nothing was used and now all of a sudden our account has a nil balance I would like to get to the bottom of this cause im disgusted