Am I wrong to ask my girlfriend to block her ex and how do I confront her?

A guy my girlfriend has been with sent her a message on Instagram and I kindly asked her to just block him and she got defensive
Then this turns into an argument and she finally blocked him
But then I noticed 1-2 weeks later she had unblocked him and followed again
Am I in the wrong to ask her to do this?
And how do I confront her about knowing she has been talking to him?
Updates
1 mo
She cheated asked her to show me the messages which should be fine if there is nothing happening but no they were exactly what I feared them to be
Am I wrong to ask my girlfriend to block her ex and how do I confront her?
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