They say if you cancel a line of credit it can reflect poorly on your score.

That is not 100% true. Canceling a line of credit can impact your score, but it depends on what you are canceling. I use a site called https://www.creditkarma.com/. Even though it can't explain the exact formulas (they are proprietary to the credit rating companies) they do a good job illustrating what is impacting your score and to what extent.