Royal Mail was fined £ 1.5 million by the regulator for being late with first class deliveries and charging customers for second class stamps.
Ofcom said Royal Mail had failed to deliver 93% of first class mail within one day of collection.
He also billed people £ 60,000 after raising the cost of a second class stamp before a price cap was officially lifted.
Royal Mail admitted to being “disappointed” with its performance.
In fiscal 2019, Ofcom found that only 91.5% of first class positions were on time.
“Royal Mail has dropped its customers, and these fines should remind us that we will take action when businesses fall short,” said Gaucho Rasmussen, director of investigations and law enforcement at Ofcom. .
The watchdog also found that the company had increased its price for second class stamps from 1p to 61p seven days before the official ceiling was lifted.
Royal Mail estimates that it has invoiced £ 60,000 from people “that it is unable to reimburse”.
Royal Mail admitted that she made a mistake and donated the money to the charity Action for Children.
“We have worked with Ofcom throughout this investigation and have learned from this process,” the statement said.
Earlier this year, Royal Mail raised the price of a first-class stamp, which now costs 11p more than second-class postage.
The price of a first class stamp for ordinary letters increased from 6p to 76p and that of the second class increased from 4p to 65p.
The second class stamp 65p is the maximum under an Ofcom price cap.
Commenting this fiscal year, Royal Mail said it would be on track to achieve the first-class delivery target of 93% without the coronavirus outbreak.
“Despite our best efforts, parts of the United Kingdom experienced reduced service levels in March,” he added.
“Relevant factors included high levels of coronavirus-related absences and the necessary social distancing measures. ”
Last month, Royal Mail announced that it would cut 2,000 management positions as it struggled to cope with the effects of the coronavirus crisis.
The reductions, equivalent to about one-fifth of the company’s executive positions, aim to save around £ 130 million compared to next year.
Royal Mail said the pandemic has accelerated the trend to send more packages and letters, and has not adapted quickly enough.