Can anyone tell me what's really wrong. I use Sprint and each time I send a text to my ex's number I receive a txt from 8353.
And what does the text from 8353 say? You need to confirm with your ex that the number you are texting is still their number.
The first thing you need to do is to call your ex and confirm that they still use that number. As regards what the text means, you would have to specify exactly what the text says. Contact your service provider and ask about this.