Solanum crispum? Vinca? Clematis? Laurentia?
There must be dozens of plants with blue star flowers, we'd need a photo and an indication of size if you want it identified.

i would guess Laurentia because I've just bought 2 plants and that is how I would describe them!

Could also be a type of Campanula..............

It could also be Lithospermum " Heavenly Blue" .

I put "Blue Star" into the RHS plantfinder search and it came up with 28 species that have a variety called "Blue Star".