Over billing

I signed up with Vox in Dec 2020 ,I received the SIM card on the 25th of Jan 2021 the SIM was then locked the 1st feb 2021 and they want me to pay for 2 months of data I have not used. I constantly ask bill me for the 5days I used the SIM card .I even have then sending lawyers due to none Payments.how can I pay for two months please make sense to me when I had the SIM card for 5days