Currently, there is no way to properly stop (or “unsubscribe” from) a bot other than blocking it. Bots can be stopped, but some still send you messages (or updates) later on in the future, most of which are simply advertisements. So, even when you stop a bot, it can still push in its updates.
If I stop or restart a bot, I don’t want to receive future messages at all. Once stopped, bots should go back to the way they were before interacting with them for the first time, thus the term “unsubscribe.” Personally, I don’t block anyone, and I tend to keep my block list empty. Right now, though, and for such a long time, my block list has been filled with bots that I had to block in order to stop them from bothering me.