OpenStack instances stuck in 'pending delete' state

Issue

• We deleted some instances and they are stuck in the pending delete state.
• 'nova force-delete ' is also not deleting these instances.

[stack@undercloud ~]$ nova delete  dummy-VM-4 
Unable to establish connection to http://<ip>:8774/v2/<uuid>/servers/<uuid>
ERROR (CommandError): Unable to delete the specified server(s).
[stack@undercloud ~]$ nova force-delete  dummy-VM-4 
ERROR (BadRequest): Instance <uuid> in task_state deleting. Cannot force_delete while the instance is in this state. (HTTP 400) (Request-ID: req-<id>)
[stack@undercloud ~]$ nova show dummy-VM-4
+--------------------------------------+----------------------------------------------------------+
| Property                             | Value                                                    |
+--------------------------------------+----------------------------------------------------------+
| OS-DCF:diskConfig                    | AUTO                                                     |
| OS-EXT-AZ:availability_zone          | nova                                                     |
| OS-EXT-STS:power_state               | 1                                                        |
| OS-EXT-STS:task_state                | deleting                                                 |
| OS-EXT-STS:vm_state                  | resized                                                  |
| OS-SRV-USG:launched_at               | 2016-04-12T15:18:54.000000                               |
| OS-SRV-USG:terminated_at             | -                                                        |
| accessIPv4                           |                                                          |
| accessIPv6                           |                                                          |
| config_drive                         |                                                          |
| created                              | 2016-03-17T06:11:27Z                                     |
| flavor                               | EcIPP-dummy-VM (<id>)    |
| hostId                               | <id> |
| id                                   | <id>                    |
| image                                | centos (<id>)            |
| key_name                             | EcIPP-key                                                |
| metadata                             | {}                                                       |
| name                                 | dummy-VM-4                                               |
| oam network                          | 192.168.2.110                                            |
| os-extended-volumes:volumes_attached | []                                                       |
| progress                             | 0                                                        |
| security_groups                      | default                                                  |
| status                               | VERIFY_RESIZE                                            |
| tenant_id                            | <id>                         |
| updated                              | 2016-04-19T19:36:30Z                                     |
| user_id                              | <id>                         |
+--------------------------------------+----------------------------------------------------------+