You will need a tracking number to follow the progress through the system.
Ali Express can provide tracking numbers for items less than £10.
The tracking number will ensure there is an actual parcel, and that ensure the parcel is en-route to your address.
Customs could be on a work to rule again if they are still in a pay dispute, so you can expect to wait up to a week for processing if they are short staffed (e.g. during school holidays).
Edit - if the delivery is to an AD, they can still provide a pdf printout of the actual progress.
If the supplier has no evidence of tracking, the alarm bells should start to ring.