Cannot remove the bootcamp partition whether with disk utility or terminal

I have been trying to remove my bootcamp partition recently. When I run bootcamp assistant, it simply does not recognize the bootcamp partition, and prompts me to create another bootcamp partition.

diskutil list

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         180.0 GB   disk0s2
   3:       Microsoft Basic Data                         70.7 GB    disk0s3
                    (free space)                         180.3 GB   -

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +180.0 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD - Data     138.4 GB   disk1s1
   2:                APFS Volume Preboot                 359.7 MB   disk1s2
   3:                APFS Volume Recovery                1.1 GB     disk1s3
   4:                APFS Volume VM                      5.4 GB     disk1s4
   5:                APFS Volume Macintosh HD            15.5 GB    disk1s5
   6:              APFS Snapshot com.apple.os.update-... 15.5 GB    disk1s5s1

I have tried removing the bootcamp partition manually with disk utility, but it tells me that it failed. Now when I try to remove it again, the '-' button is grayed out, like this: 

I have also tried sudo diskutil eraseVolume JHFS+ drive disk0s3 But the following message appears:

❯ sudo diskutil eraseVolume JHFS+ drive disk0s3
Password:
Started erase on disk0s3
Unmounting disk
Error: -69879: Couldn't open disk

And the error message 

Error: -69879: Couldn't open disk 

appears every time I try to do anything related to the bootcamp partition.

By this time my whole disk is just messed up. Any help is appreciated, thanks.