What to do if orthodontic retainer not working!?

Depends: Sometimes if wearing a retainer inconsistently, the teeth shift and the appliance will no longer fit. I would return to the Dr that gave it to you and ask specific questions.

Call: Call your Orthodontic Specialist. If teeth are moving it means either you are not wearing retainer enough hours per day, or it means it needs an adjustment. Make an appointment to have your occlusion and your retainer checked and, if necessary, adjusted or replaced. As an aside, please know that there is more post-treatment instability if Rx done by GP, and if alternative appliances were used.

See your orthodontis: Likely is do to not wearing consistently. You may require that a new one is made. See your orthodontist to determine exactly what needs to be done

See an Orthodontist: If you do not wear orthodontic retainers as prescribed by your orthodontist then your teeth will go crooked again, and the hard work in wearing the braces will be lost. The reason for wearing retainers is to keep teeth in place after dental braces. If concerned, see an orthodontist.