Most supermarkets in holiday areas are open on Sundays during high seaon (July to end of August) but usually close earlier.
The Eroski at Nueva Condomina has closed down but there is an Alcampo on the other side of the motorway at the Thader centre. If coming from Alicante airport come off motorway as if going to Nueva Condomina and follow the road until you see the left turn at a roundabout signposted "Thader ".
Not sure if Alcampo is open Sundys and website not very clear re opening hours. Maybe someone else can help re this.
I think Consum at Camposol is open until either 3 or 4 if this helps.
Jean