Over billed

My daughter turned 21 in August and recieved a letter from Sizwe stating that if my daughter is a full time student I should provide a proof from her institution,or else I will be billed on adult rates as she is one of the beneficiaries. I have submitted the documents on 04/09/2018,but my monthly contribution was increases by R1100.I first queried to HR which referes me to Sizwe. They told me they have recieved the docs and they will rectify the error and refund me, but Im still waiting for the refund till today.