Cannot delete stack after update failed

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I tried to update an existing stack by just changing a parameter setting the number of server groups but it failed due to exceeded server group quota.
I then tried to delete the stack but it failed, heat-engine.log show the following error

2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource Traceback (most recent call last):
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/resource.py", line 770, in _action_recorder
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource yield
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/resource.py", line 1707, in delete
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource *action_args)
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/scheduler.py", line 352, in wrapper
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource step = next(subtask)
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/resource.py", line 823, in action_handler_task
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource done = check(handler_data)
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/resources/stack_resource.py", line 549, in check_delete_complete
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource return self._check_status_complete(self.DELETE)
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource File "/usr/lib/python2.7/site-packages/heat/engine/resources/stack_resource.py", line 415, in _check_status_complete
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource action=action)
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource ResourceFailure: resources[0]: resources.pairs.Resource DELETE failed: resources.core: Stack DELETE cancelled
2017-12-18 23:34:37.755 10017 ERROR heat.engine.resource

Which is strange because all other stack command succeed

Any idea what could cause this problem

SM

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