The /Ɵ/ sound is spelled with <th>. The /ŋ/ sound is spelled with <ng>.
This is a contrast between a voiceless dental and alveolar fricative and a voiced velar nasal continuant and can only occur finally. It is not a problem, although the sound /Ɵ/ is difficult for many learners.
doth dung Goth gong hath hang Kenneth kenning kith king pith ping withe wing wrath wrong wrathful wrongful wrathfully wrongfully