It may be that complaints submitted over the bank website are handled by a different (more responsive) team than complaints made at the branch.

A lot of times, when it comes to business like this, in person complaints go into the ether, but the online complaints are recorded and play a part in performance metrics, or hit corp response team rather than branch.

This is it. Online complaints will go into a system where they are monitored by (very) senior management and reported to regulators.

Now if only Google had a similar complaint form.