Cadbury has never been real chocolate. If you really love chocolate with cacao butter and not some artificial WW-II inspired junk, look to Belgium or Switzerland.
INGREDIENTS: SUGAR, MILK SOLIDS, COCOA BUTTER, COCOA MASS,EMULSIFIERS (SOY LECITHIN, 476), FLAVOURS. MILK CHOCOLATECONTAINS COCOA SOLIDS 26%, MILK SOLIDS 24%. ALLERGEN STATEMENT: CONTAINS MILK AND SOY. MAY CONTAIN TRACES OF PEANUTS AND TREE NUTS.
https://www.cadburykitchen.com.au/products/ingredients/cadbury-melts/
The bars you bought may be past expiry date or were stored in sub-optimal conditions. YUCK!!