With held funds on my account

Very disgusting service from FNB, I have received a refund yesterday from SARS after my annual tax assessment. This morning FNB decided to with-hold the funds and send a request to SARS for verification as the deposit triggered some risk within the bank system. I was relying on this fund to buy food for the family and now have to go hungry because of FNB system and suspicions of the refund made by SARS to my account. This doesn't make sense as SARS is a reputable institution.