Telkom over deducted money and refuses to refund their customers

In June 2018 Telkom overcharged me with R201.75, Which they refuse to give back. One of their sales agent suggested that I deduct that amount from my payments which I only did in January this year. Telkom the disconnected my service although they have send me a statement showing this credit on a statement/account of mine They refuse to give it back to me