If anyone is hurt, call 999. Everything below is for the other case — the car is stuck and nobody is injured.
What do you try before calling anyone?

Four steps, no tools. Most vehicles come out on those alone, and the full method is here. Pump the tyres back up before you drive on tarmac.
Who comes out if that doesn’t work?
Three different things, and they are not interchangeable.
- 999, if anyone is hurt or the situation has stopped being about the car. What to say when you call.
- Your own convoy. The people already with you reach you in minutes rather than hours. It is the whole reason the convoy rules exist.
- Volunteers and paid recovery. Volunteer groups drive out on their own time — nobody is on duty and nobody is obliged to answer. A recovery company will come for a fee.
How do they find you in the dunes?
By your coordinates. A place name will not do it: dune fields have no addresses and look the same for kilometres, so the area you would name covers far more sand than anyone is going to search.

The app opens WhatsApp with your exact position already written into the message. You press send yourself. GPS keeps working with no signal, so you can know where you are before you have a bar to send it with.
Get the app to send your position
What do you do while you wait?
Stay with the vehicle. It is far easier to see from a distance than a person on foot, and it is your shade. Raise the sand flag, and after dark put the hazards on. Drink before you feel thirsty — heat is what turns a stuck car into an emergency.