Here are some tests that helped me figure out what was wrong with my program:

316496
out => 317559 317560

318533
out => 318659 318660

945999
out => 950509 950510

055099
out => 055109 055110

00510059
out => 00504999 00505000

00450010
out => 00460019 00460020

00504010
out => 00504999 00505000

0019
out => 4509 4510

00510059
out => 00510059 00510060

945999
out => 950509 950510

008359
out => 009449 009450

3000
out => 4509 4510

4509
out => 4509 4510

4099
out => 4509 4510

9999
out => No solution

373730020389
out => 373730021389 373730021390

373730030290
out => 373730031289 373730031290

373730030289
out => 373730031289 373730031290

Good luck!