Data not been loaded

My husband has a contract with my Mtn the contract was a black Friday deal R299 for 120g of data 60night and 60day Every month we have been only receiving 40gb it went unnoticed until now because of the amount of data we are using during this time of the lockdown The sms received by mtn every month confirm the same so why is mtn robbing us and what is happening to the data for the last 18months of the contract. It went unnoticed so wasn't corrected I would like a response from Mtn and what are they going to do about this..tried calling them and there was no answer.terrible service