A seven-year-old with Strep A was abandoned by the 111 service on Christmas Eve after they told her mother they were too busy to assist them.
Mother-of-two Hannah Tonge's seven-year-old daughter Chloe developed a fever, sore throat and swollen glands on Christmas Eve.
After holding on the phone to reach a 111 operator for an hour and twenty minutes, Miss Tonge, 35, of Falkenham, near Felixstowe, decided to hang up as Chloe was showing signs of recovery following a dose of Calpol.
"On Christmas morning, she picked up quite a bit," said Miss Tonge.
"But it was around mid-afternoon that she started to go downhill fast. We were really worried."
Chloe was quickly developing common symptoms of Strep A - lethargy, swollen glands and red spots in her mouth.
Her mother requested a 111 call-back via an online form and they were given an estimated wait time to speak to a nurse of six hours - a call they would never receive.
"A lovely man called to explain that they had received an exceptional number of requests," said Miss Tonge.
"I gave him Chloe's symptoms and I thought she would be moved up the list, but I was wrong."
In desperation, Miss Tonge called her father who advised that they may be able to access healthcare through the family service on his private plan.
Within an hour and a half, a private GP had diagnosed Chloe with Strep A and prescribed her a liquid form of penicillin which Miss Tonge easily found in a Felixstowe Boots pharmacy.
Assuming that Chloe's NHS files had been updated and the 111 request had been overridden, Miss Tonge thought nothing more of the call until she received a text a couple of days later.
On Wednesday, December 28, three days after she had initially requested help, she received a text saying "due to high demand we are unable to assist you".
Miss Tonge said she felt "so let down," adding: "I was really shocked and fear for those who weren't as lucky as us with the private insurance."
An NHS East of England spokesman said: "While NHS 111 provision in Suffolk is provided by a third-party supplier, we will be investigating the case fully and in cooperation with the local provider to understand what happened on this occasion."
Read more: Strep A: All you need to know from symptoms to treatment
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