How to deal with harassing phone calls and text messages when selling invoices? . . .

To deal with this kind of short message harassment, I suggest that they take their mobile phone number to register with bad websites, and give them a verification code for a while and a verification code for a while. I don't believe they're not bored! Like that kind of personalized signature, mobile phone registration website and so on. The best way is to always register with their mobile phone number, so that he can always receive the verification code and deal with him as he deals with you!