The 80-year-old alerted South West Water to the rat problem after his wife Sylvia and neighbours had spotted rodents in their back gardens.
But shocked OAP Vern Glasspoole said the company told him to go down into the sewer and get rid of the unwanted guests himself.
Mr Glasspoole said he was told to climb down the manhole outside his home in Marina Way, in Tiverton, to get to the rats.
Mrs Glasspoole, 84, said the problem had got so bad, she was struggling to sleep.
She said she was kept awake at night by the sound of rats gnawing the side of their home.
She also said the couple’s pet dog Quincy had become anxious about the rodent problem.
Mrs Glasspoole said: “I could hear it and I kept worrying it was going to some how get into my room.
“The dog is scared stiff, I’ve never seen him like it before.”
Mr Glasspoole, a former technical engineer for computer giant IBM, had also contacted Mid Devon District Council about the problem.
But he said council staff simply passed him onto an external pest company.
A spokesperson for South West Water said: “We would never advise a customer to go down into a sewer or climb into a manhole.
“Sewers and manholes are hazardous places and South West Water staff must have confined space entry training and specialist safety equipment before being allowed to enter them.
“Our records of Mr Glasspoole’s telephone conversation with our call centre on 9 July show he was advised it was very unlikely the rats had come from the sewer. Rodent infestations are the responsibility of the owner or occupier, so he was advised to contact a pest control agency to deal with the problem. He was also advised that his local council may be able to assist with this for a fee.