Brush twice a day and floss teeth, enamel is warring away and gums receding, why? I do not eat lots of sugar etc

Trauma. Los of enamel often associated with traumatic insult such as brushing too hard, using medium or hard toothbrush, abfractions from malocclusion, fractures from chewing hard things like ice/hard candy, pernicious habits. See your Dentist for evaluation and advice.
Hard Brushing. Brushing hard with abrasive toothpaste or medicaments can cause enamel abrasion and gum recession. Regular visits to your dentist will monitor your overall oral health and allow your dentist to make recommendations for corrective care.