I did a similar service but had to shut it down because people were using it to spam other people.. basically send stupid texts by putting in their friends numb

I did a similar service but had to shut it down because people were using it to spam other people.. basically send stupid texts by putting in their friends numbers. I would get complaints because of limited texts or txt do cost money and this was an issue of reoccurring texts. I haven't tried your product but how do you solve this problem ?