Why does my ex has my contact number?

So it's been a year since we broke up, then we tried to keep it as a friendship obviously but it didn't work out. So after 5 months of absolutely no contact, I deleted him from social media and his phone number, I found I kinda still had his number [my bad!] In an old journal I had and I was writing down some phone numbers because I changed my phone. Anyways, out of curiosity, I added him back but hide my whole info [so he couldn't see that I added him back on whatsapp]. Truth is, I'm still able to see absolutely everything from him, and he's a pretty reserved guy. He told me he didn't want to have anything to do with me and so did I. Why would he have my number still? [BTW, I deleted his number again!] Any opinions? Or thoughts?

Why does my ex has my contact number?
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