Telephone company TPG has been fined $400,000 in the Federal Court for failing to give customers access to the triple-0 emergency service.

Sharon Merrin of Brisbane tried to call triple-0 after her husband had a heart attack in 2011.

She could not get through and later discovered that TPG had cut off access to the emergency service number because her phone bill was in arrears.

Her husband died three days later.

An investigation by the Australian Communication and Media Authority (ACMA) revealed there had been another 193 failed emergency calls from 100 home phones.

ACMA said TPG failed to ensure the service was available to nearly 6,000 telephone services.

It is the first time a phone company has been prosecuted under the Telecommunications Act, which makes it mandatory for them to maintain access to emergency calls.