John Slinger MP at the Rugby Royal Mail sorting office.
People in Rugby say urgent action needs to be taken to tackle missed or delayed postal deliveries across parts of the town.
They say letters have been arriving weeks late, post is not being delivered for several days at a time, and large batches of mail are turning up all at once.
Residents are frustrated over the service they are receiving from Royal Mail.
Heidi Thomas, of Boughton Vale, said: "I was kept waiting weeks for some important letters.
“They were finally delivered while we were away and now I’m drowning in post. It’s very frustrating when post is not delivered in a timely manner.”
Alan Hunt, who lives in Bilton, said he was also kept waiting.
He said: "After weeks without any post, I got home to 27 letters.
"I managed to get through to Royal Mail after two hours on the phone and raised a complaint. They said it was due to staffing issues. I’m not impressed.”
Rugby MP John Slinger said people are missing important appointments as a result and described the situation as “completely unacceptable”.
He said: “Despite having raised this issue with Royal Mail several times, the issue persist and is not yet fixed.
“I will be raising this in Parliament and taking this up with ministers.
"Constituents have let me know about some letters arriving almost a month later, for one constituent this included important letters from their bank, HMRC and pension company - all of which arrived alongside a number of other items. It is easy to see how things can go wrong, very quickly, if letters like these don't arrive on time.
"When I heard about this, I immediately raised it with Royal Mail. However, their response has been unsatisfactory. They explained that letters are grouped together according to their delivery targets and delivered on a specified day. That does nothing to explain why a letter from a bank should take almost a month to reach its customer.”
The MP praised the postmen and said the issue wasn’t about them.
He added: "It is Royal Mail’s responsibility to ensure that the mail arrives on time, and if they need to invest more money to ensure that there are enough delivery rounds then they should do so. They can't just simply rely on grouping letters together to save the postie a few extra walks up a garden path.
"Waiting almost a month in some cases for important correspondence from banks or the NHS is totally unacceptable, and I will continue to raise this issue at the very highest levels of Government.”
We have contacted the Royal Mail press office twice for a response about the delays. They have not replied yet.
On their website, it states: “We aim to deliver to all addresses we have mail for, six days a week. In a small number of local offices, this may temporarily not be possible due to local issues such as high levels of sick absence, resourcing, or other local factors. In those cases, we will rotate deliveries to minimise the delay to individual customers.
"We also provide targeted support to those offices to address their challenges and restore our service to the high standard our customers would normally receive.
"We're sorry for any inconvenience and thank you for your understanding.”