Delays to postal services in parts of Staffordshire has seen residents collect their male from the sorting office themselves or get it delivered in one big bundle.
One woman from Lichfield said she went three weeks without a delivery, only for a big parcel of letters to arrive after she contacted the sorting office.
A couple from Rugeley said they had been to the sorting office eight times this year after going weeks without post and that it caused problems with hospital appointments.
Lichfield MP Dave Robertson said hundreds of frustrated constituents had been in touch over the issue. Royal Mail acknowledged problems and said it was working to recruit more support to improve service.
Jean Russell, 91, has lived in the Netherstowe area of Lichfield for 25 years and said she relied on the postal service.
She told BBC Midlands Today she had not received any letters since 29 November, and felt the service had never been so poor.
"I went three weeks without any post at all, from the middle of October, and I decided to contact Royal Mail customer services.
"Lo and behold, the next day a large parcel of post arrived."
Karl and Lin Kozurek who live in Rugeley said they had visited their sorting office eight times this year after going for weeks without any post.
They said when they had complained a large bundle would usually arrive the following day.
"We have doctors and hospital appointments coming through but they're just quite late, quite close to the appointment time, it doesn't give us much time to react really," Mr Kozurek said.
"It's got worse over the last three or four months in particular."
"The universal service obligation is the requirement that Royal Mail have to get your first class letters, or a percentage of them, to you the next day," Robertson said.
"That's currently what's not happening in Lichfield."
He added: "Unfortunately [people] are being let down by a system and a company which just isn't meeting its obligations to the people."
A spokesperson for Royal Mail said recruitment was under way, and extra support was being brought in to improve the service.
They added teams were working hard to provide a reliable service as they moved through the busy Christmas period.