Outages have been widespread, from south of Colbinabbin to north of Wyuna across Wednesday, Thursday and Friday, and it is expected to continue for at least another two days.
It's left people without reception for as much as 12 hours each day.
Telstra doesn’t directly control EFTPOS machines and some can be switched to Wi-Fi, many use 3G and 4G networks to operate.
Messages were sent out to residents saying upgrades would be taking place, and "your mobile service may be impacted at various times during this period".
It’s caused chaos for businesses like Dee Stagg’s Wickedly Deevine, who has been unable to use the EFTPOS machine for two-and-a-half days and has begun taking orders on a tab.
“It’s made life very difficult,” she said.
“We have no banks at this end of town, people at the other end of town can say ‘oh I’ll just nick down to the bank’, which they can do because they’ve got three. We’ve got none.”
She said the messages sent by Telstra before the planned works commenced didn’t make it clear service would be down for an extended period.
“It hasn’t turned people away but we’ve let customers run a tab because we know most of them but I added it up then, there’s $148 of sales on those two pages and that’s not money in the bank I can pay a bill with,” she said.
Ms Stagg is also the president of the Kyabram Chamber of Commerce and said businesses across town were widely affected in a variety of ways, from rostering to contacting staff to paying wages.
She said it was a busy time for businesses, with dozens scheduling sales.
“A lot of businesses are running sales at the moment due to the Buy In Ky promotion so you’ve got a lot of people wanting to come into town and spend money,” she said.
Society Café employee Darianne Scapin said it had been “a little frustrating” asking people to pay with cash.
“It is a little frustrating. I don’t think people realise how much they rely on (EFTPOS), we’ve gone back to the old way of people having to carry cash on them,” she said.
She said most people had been understanding and happy to go and get cash, but said it wasn’t ideal to make a second trip to withdraw money, especially for older residents.
Resident Hayley Bennett said the outage was affecting her and her family in "a lot of ways".
“Let's hope school/kinder/family don't need to contact for an emergency,” she said.
“The text message we got from Telstra stated we ‘MAY’ experience problems. Not we will experience nothing from 8 am till 6 pm daily for five days."
A Telstra spokesperson said the upgrades at the Bradley St tower required switching off antennas and services to build the new infrastructure required for 5G upgrades.
“There’ll be some full-day and some half-day disruptions,” they said.
The spokesperson said the work needed to be completed during the day, and upgrades would continue until the end of June.
“We need to work during the day because our crews will be working at height, so there’ll be some days we need to switch services off, while at other times we’ll be working on different parts of the upgrade so we might only need to interrupt services for a few hours.
“We’ve sent out text messages to customers in the area so they’re aware of the planned disruptions.
“We know there’s never a perfect time to schedule upgrade work and we apologise for the interruption but once we’re finished, we know customers will notice a big difference and improvements to their mobile connectivity.”
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