Can't delete bootcamp partition.

In Terminal, run

diskutil eraseVolume jhfs+ BC1 disk0s3

diskutil mergePartitions jhfs+ BCMP disk0s3 disk0s4

diskutil list

If you only see disk0s3, then run

diskutil eraseVolume fat32 BCMP disk0s3

and re-run BCA and click on Remove/Restore. Stop if you see any error messages and post the Terminal session.

You will have to repartition and format the entire drive.

Internet/Network Recovery of El Capitan or Later on a Clean Disk

If possible backup your files before proceeding.

1. Restart the computer. Immediately after the chime hold down the (Command-Option-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the drive (usually, the out-dented entry) from the side list.
5. Click on the Erase tab in Disk Utility's main window. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Reinstall OS X and click on the Continue button.

Note:

1. To install the version of OS X that was currently installed use Command-Option-R.

2. To install the original factory version when the computer was new use Command-Option-Shift-R.

From macOS Terminal, post the output of

diskutil list

Excellent. Please remember to back up macOS.