Inconsistency of transliterating in iso-233-3 (Arabic/Persian simplified)

letter ‬‬چ‬‬ is once transliterated to c

and latter transliterated to č

I understand shadda doubles the letter, and apparently it underlines it too, but the letter itself is different

would be great too if we can confirm shadda rule, specially for letters having a symbol under it like ḥ ح for example

interscript / maps