First please check the Royal Mail tracking for your parcel.
If the order is showing as still out for delivery after 3 days, then please contact blu Support.
If the order is showing as delivered but you have not received your order, then please first check around your property and check that it has not been delivered to one of your neighbours. Failing that please contact Royal Mail quoting your tracking number and lodge an investigation with them. Notify blu support with your Royal Mail case number.