So I'm going to preface this by saying that I can't find the full context of what is going on but I see you saying that you got something from someone else's Instagram and that you're being accused of pretending to be someone.
This means you've used images of someone else's likeness or their art without their permission and they're extremely extremely upset over it. You're making excuses of being "a fan" to justify it.
As someone who has had this done to me before it is extremely uncomfortable and in some cases violates copyright laws to take someone else's photographs (art) or art and repost it without consent.
It's wrong they're harassing you, but it's not wrong for them to be upset. It's wrong for you to not consider their feelings and their legal rights when it comes to reposting their intellectual property without consent.
They have every right to file a DMCA takedown notice with the host of wherever their stuff is posted. You can file a counter notice if you disagree, but they can file a civil lawsuit against you if you do. The host is also within their rights to ban you for violating other people's intellectual property rights.
It sucks this is happening to you, but it's not okay to violate others intellectual property rights. I advise taking down their work immediately, be the bigger person, and post an apology where they can see it. There's a high chance they will leave you alone after you do so. /gen