I just upgraded from a Samsung Galaxy s5 to an s6, kept the same phone number and both were/are on Sprint, and some of my text messages are randomly still going to my old phone. I called customer service yesterday and they had me type in the code to make sure it was fully programmed on the new phone and the old phone was deactivated, and I still am having this issue. I will get most texts on the new phone, and then suddenly, from the same person, one ONLY shows up on my old phone. The only common thing I can figure out is that all of the texts that are going to the old phone are from iphone users...but again, it only happens very occasionally, and most texts come through to the new phone.
was your old phone sync'd with either google voice or hangouts?
if youre old phone is connected to wifi right now im willing to bet its still connecting to hangouts and pulling some of them that way. disable it on the old device..
SMS was already disabled on Google Hangouts on the old phone 😕 That was a great thought, though.
no worries..since it doesnt have a data/voice signal anymore that can be the only reason its still happening. over wifi..since texts dont come through wifi Google Voice or hangouts would be the main culprits i can think of that would cause it.