There must have been some evidence that you we asked by your boyfriend to smuggle contraband. Whether the letter was read or they overheard a conversation on the telephone (they listen to and record every call) you were singled out as a potential problem. They cannot arrest you for something that was asked of you, that you didn't actually carry out.
https://www.inmateaid.com/ask-the-inmate/my-boyfriend-is-in-smci-he-wrote-me-a-letter-asking-me-to-smuggle-in.amp#answer
Accepted Answer Date Created: May 14,2016