Parcel never got delivered to me

I ordered vitamins online and you never delivered it, I was home the whole day you were supposed to deliver. When I checked the app to track the delivery, it said it was successfully delivered and it even stated that I signed for the parcel, which is not true. I have now logged 3 separate queries on different dates since the 10th of August, your agents keep telling me they will investigate it but nothing is happening and I am not getting any feedback. I want a full refund on my order as clearly your courier delivered it to a wrong address. Please sort this out urgently! I have been a loyal customer and I buy almost weekly from you since you opened, but this is the worst service I have ever received. Please can someone refund me the full amount, so I can re-order my vitamins again.