Dissappearing Data and no response

Every month on or after the 28th, either my "unlimited" calls are finished or data finished. I was surprised as I use wifi everywhere i go. I received the usual message data is finished. I quickly checked my balance. I seen i had 4.25 gigs left. I continued to check for about an hour, which remained 4.25 gigs. Then all of a sudden, it went to 0. I stayed without data till the 7th renewal. Then they send me a report which shows Tiktok usage which I dont have the app on my phone. I took screenshots. I sent it Melon mobile. I ask them everyday, still no response. Im not entirely unhappy about them, they have fast responses, but I feel they have irreegulatries in their system software and i dont trust their reporting.