Hello Claire.
The first thing I would do is to check the fuses- this will be in a panel just below the dashboard on the right hand side. Presumably from your post it is neither unlocking from the remote or from the key.
If all else fails- and it's a bit of a pig of a job- if you climb into the boot and remove the plastic trim on the tailgate, you can see the locking mechanism and you might be able to pop that open. My Astra doesn't have a deadlock on the tailgate, but if yours does and the CL isn't working that might remain engaged- if so then it's finding the wires and locally applying power to it.
First thing to do though is check the fuses. Always the fuses.
Let us know if that doesn't solve the problem.
Derek