Billing and poor service

DSTV -I took in my decoder due to the error it had which is 8118 upon my arrival i was told that l needed to replace my decorder . I paid R349 and asked to move my payment date to the 15 .of which the lady confirmed to had done so . When I got go i found out that my account ws suspended and I was to pay R555 instead of R399 . I then called the call center only to be told that I was going to be contacted till date .I wasn't to know why l have a strange amount added to my account