The confusion is caused by the way Sanskrit is transliterated/romanised. The anusvāra is represented by an m with a dot underneath it - 'ṃ'. This is pronounced according to its surroundings. When it precedes consonants from the five rows of stops i.e क varga, च, ट, त & प varga - it is pronounced as the 'varga' nasal - which means गंगा is गङ्गा, चंचू is चञ्चू , रंजन is रञ्जन, दंत is दन्त and पंपा is पम्पा I
I'm eternally grateful to Dr. Renate Sӧhnen-Thieme not just for her help in understanding this topic, but for helping me realise how precise Sanskrit is.