wrong billing

for the past two months i have been receiving sms's from the service provider stating that i have an outstanding balance of R507.01 even though i have been paying each and every month since taking out both contracts paying access amounts of close to R700 for contracts that are less then R500. i spoke to two agents saying its an error but now i got an sms saying i have been handed to lawyers by the name of Fourie Sikweyiya referrence number TS10027.on the 16 and 17 /03/2015 its rather worrying when lawyers get involved i will need this matter to be fixed or will take steps that will resolve matter with the ombudsman.