COMPLAIN ABOUT MOBICEL

I am very disappointed with mobicel,my child needed a tablet for schooling so I've decided to buy her a mobicel tablet after a month the tablet had a black dot ink on the screen i asked her what happened she said it shutdown then went back on with the black ink on screen , i thought she was lying but she came home with 3 students using the same model table to show me that their tablet has same problem so i took photos of the tablets and email it to mobicel to show them their tablet, they said it was my fault i asked them how can 4 tablet and same model experience the same problem and all student bought it on January 2020 ,so now they said i must pay the money so that they can fix it, I'm so very disappointed