Try replying to the message with the word "STOP" this usually works if its a message coming from advertisements or businesses that wants you to buy something or participate in something that they have advertised on TV.
I recently switched from a Delve to a Droid. I too have been inundated with texts from 6633423. This is an inactive number from Mudlake, Idaho. I know because I called the number and got a recording stating this. I then called the Mudlake telephone company only to be told it is an inactive number because their numbers are 6634... We went in circles. If it is inactive how can it send texts! Bottom line they were no help. I have tried texting 'STOP', I have tried blocking the number. Verizon says I may have to change my number. Not a desireable option. Somewhere there is a device that is plugged into a power source and sending out these texts. As there seems to be so many people receiving this unwanted giberisf, why don't they pull the plug?!
I had a problem with alerts when I first got my Blackberry. On my old non-smart phone, I had the $5 / month email service where I could send/rcv emails from my POP3 email accounts from the phone. That service would notify me when I had a new email.
When I upgraded to the Blackberry, I would get the strange txt messages (do not remember the specifics of the message) that I tracked to my email.
The only way I got them to stop was to change the password on my POP3 email so that the old Verizon mail service could no longer check for messages.
That fixed the problem right away!