At first look, I am guessing that the serial number is fake. I could be wrong but only Autodesk can tell the truth.
None here can know what your activation code is as the forum members are AutoCAD users, not Autodesk employee. You may have to contact your local Autodesk reseller - the place you purchased AutoCAD license.
HTH
Please mark "Accept as Solution" and "Like" if my reply resolves the issue and it will help when others need helps.
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A circle is the locus of a cursor, starting and ending at the same point on a plane in model space or in layout such that its distance from a given coordinates (X,Y) is always constant.
X² + Y² = C²
