ATM retained my R200 note

Good Day, I deposited cash into the FNB ATM 27 September 2017 and it retained R200. I went into the branch to report this and was assured I would receive a phone call from their custodian and be returned my money. This did not happen, so the following week I went back to the branch and the same consultant assured he would look into it. Then again I received no response or anything. Its been 2 weeks now and I have not received the funds. This is R200 that was retained from me? This money belongs to me and not the bank so I don't understand why it is taking so long for FNB to pay this back?? This is essentially theft and I would like an immediate refund. I have also been a loyal customer for a decade (probably more) and this is the service I get? Unacceptable FNB.