Telegram has done an amazing job of this compared to basically everybody else. Anybody can create a bot in a few minutes and they are full featured. You have to initiate a chat with a bot for a bot to be able to interact with you and you can block them at any time. (I'm sure they have some internal metrics that also intervenes for bots that are getting blocked a ton)
Compare this to anybody else and it is head and shoulders better. WhatsApp is launching bots, but they will be paid, they can reach out to you without you interacting with them and they will be heavily policed. (IE, you will need to get approval from WhatsApp to launch your bot)
They have also made hosting be a problem of aggregators like Nexmo, Twilio and Clicaktell. So you need to pay them as well. Clickatell is advertising over $1,000 a month to host a WhatsApp number.
Bananas and a total shame. This is the kind of walled garden bullshit that makes me sad for the internet.