Did you find it in an original email or it was in the text file you created?
If you find it in an original email, it's high likely that it's a scam because it's wrong from the beginning.

but if it in the text file you created, The mistake might be that you recorded it incorrectly, for example You may alternate lowercase letters with uppercase letters. (Base58 is case sensitive), The more mistakes you make,the more time it takes to find. It may take an hours to find valid key in 3 letters wrong. But for 4 letters wrong, It may take months or even years to find the valid key [Run on one simple CPU 24hr/day]
In this case, I think the first thing to do is you should try to find the private key form your original email.