Why do people in Tamil Nadu spell "Telugu" as "Telungu"?

 In Tamil, words are formed with certain rules.

We have 18 consonants. Divided into 3 broad classifications.

Hard Consonants: ka sa da ta pa ra (vallinam)
Soft Consonants: nga ngga nhha na ma nha (mellinam)
Eternal Consonants : Ya, ra, la,va, lha, zha (idainam)

First letter “Te” is a Hard Consonant. Second letter “lu” is from an eternal consonant. As a rule, third letter “gu” should be preceded by a soft consonant “ngu”.

For Tamils, Telungu works well in his tongue.