BILLING FOR 2 X BOXES , 1 X RETURNED , OTHER TECHNITION TOOK

I cancelled my subscription in AUG 2021 with VOX Telecom as I was unemployed and could not afford the payment any longer. I then get a bill of R4000 saying i owe them for 2 x boxes. I inform the lady the technition took the one bo cos he swapped it out when i downgraded my speed for 20 to 10 speed. I returned the box i had took all the other routers with to their offices in Krugersdrop. the lady said they just need the black box. They did not dedut it from my account and they are still charging me for an extra black box and says its my word against the technitions word. so where is their paper work filing system? how can i return only 1 box n not the other? this is going to go viral i will put them on tik tok and all the other social media platforms.