If texts from BusyTel stopped arriving
Replying STOP to a text tells your phone company to block every message from that number. It is their switch rather than ours, which makes it the one thing about your account we cannot change for you. Sending START from the same phone turns it back on.
If you want them to stop
Reply STOP to any text from that number, from the phone you want it to stop on. Calls to your BusyTel number are answered either way. What stops is the texts telling you about them.