Residents were shocked to find their post office had suddenly closed down.
Customers turning up to use the Seaford main office in Church Road on Tuesday were greeted by closed doors and a note saying it would be shut until further notice.
Lewes MP Norman Baker received a flood of worried calls about the post office, which serves 20,000 residents.
He said: "The post office assured me it would only be closed temporarily, but what about all the pensioners turning up to cash their pensions?
"I am horrified they have not reopened it straight away. This is unacceptable.
"It appears the post office was closed after an on-the-spot audit."
He said a portable cabin should have been installed and staffed to cope with the period of closure.
A Post Office Counters spokesman said he regretted the closure but hoped the problems would soon be resolved.
He said: "The post office had to be shut due to unforeseen circumstances and we can't predict how long it will be shut for.
"We cannot give specific details as to why it had to be closed but we are making every effort to get it up and running as soon as possible."
In the meantime, customers are being asked to use branches in Claremont Road, Vale Road and the Chyngton estate for their post office services.
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