Negligence on customer's personal details

I app**** for a change of ownership for a decoder. 6 days down the line I received a WhatsApp message from someone I don't know claiming that he had my details. The person even forwarded to me the very form I submitted with all my personal details, that is name ID number, bank details etc. I lodged a complaint with dstv multichoice but they haven't responded save for their auto response acknowledging receipt of my emails. Am scared who else has my details