breach of cofidence

I called mtn a few days ago to request for a sim swap. The guy helping me was very friendly which I was happy about... To my shock, a few days later I got a whatsapp text from this guy... When we call in call centres we are required to give our personal details i.e. ID no. Now I am very upset that the agent took my number and texted me... What other information do they take for their personal use...