Bad service and refuse to pay back deposit

I was on a month-to-month contract at Pretoria North branch, when i was supposed to leave i put in the notice as per our agreement but my deposit was never paid because they said i didnt put the notice, even after giving them all the proof they still refused, i think this is a bad service because they ****ming deposit of customers. even during the period of renting at some stage they will lock the storage even if you paid and i have to go to office and inform them i dont know my storage is locked and i submit proof of payment thats when they unlock. i think there is a problem with balancing of books. Not recommended at all.