Why ask number if you have no intention of helping?

I have contacted Vodacom on Messenger in trying to get my number they deleted back. I commented on FB regarding their use of a bot and suddenly, after 5 days, they communicate again on Messenger. After a while asking my number - i give my number, thinking they want to check that i am who i am, and i got feeling to assist me. Then realised i have the nr i am using, they want my deleted nr. I gave that. Hour's after silence they say they still won't help. Why did they then want the number? I feel very uneasy about this.