For analog cable:
If you call to unsubscribe or cancel service(s) and the cableco does not filter/disconnect services, that's on them and not stealing IMO. If you don't call... then yes, that's theft of service.
For digital cable channels:
Channels that the cableco does not want anyone to receive for "free" are encrypted at the head end. So, if you get them... (without using a illegal device/"black box), apparently they don't care and anyone with a QAM tuner can receive them. Getting VOD unencrypted is quite "normal" in many areas. Although, many times, you only get to watch for a few minutes sometimes since the channel(s) get frequently/dynamically reassigned. Also, you may have to suffer watching someone fast forwarding, rewinding, pausing... etc.