Police have issued a warning to Victoria’s Mandarin-speaking community about a fake doctor scam responsible for stealing tens of thousands of dollars from some victims.

Detectives said the fraudsters were using the victims’ names to appear credible before instructing them to buy gift cards and provide the code via text message, with the voices of doctors, general practitioners and surgeons being their most used choices.

Ten reports of the scam were received last month, including from one victim who lost $50,000 to the scam after buying gift cards across a three-day period before they became suspicious. Most victims were repeatedly pressured into buying more gift cards until they had lost almost all their cash.

Cybercrime Squad’s Detective Acting Inspector Eleanor Vallas urged the Mandarin-speaking community to remain vigilant and to call police if they fell victim to the scam, and also to keep records of any phone calls they have about their health, including screen shots of any messages.

Private colleges have issued nearly 3,000 last-minute enrolments to a diploma course that is being cancelled after allegedly being “misused” by non-genuine students, as Labor threatens to suspend providers that are manipulating new rules.

Guardian Australia revealed in September that private colleges were offering discounts to rush students into the graduate diploma of management (learning) ahead of its deregistration on 5 October, which the government says was being used by some non-genuine students to remain in the country. The assistant minister for international education, Julian Hill, said at the time the system had been “misused”.

The regulator says since the ban was announced on 4 September, more than 1,300 new enrolments had been issued and more than 1,500 students have had their future enrolments brought forward. Some immigration education agents have offered promotions for the month of September, including in WhatsApp messages and texts, encouraging students to join the course or those who have a future enrolment to study now. Several ads promote discounted course fees or a free certificate of enrolment to join immediately.

As part of the rule changes, students who have “packaged” a lower-level vocational course with the graduate diploma will need to enrol on to a higher-level course to meet their visa requirements. By fast-tracking the start date of the graduate diploma, that could mean studying two courses at the same time.

The Department of Home Affairs has issued letters of concern to several providers asking them to explain their behaviour and practices. Hill also stated he was prepared to use powers not previously exercised on colleges that have breached the rules, preventing them from being able to recruit new students.

US President Trump is considering banning diesel exports as his domestic support wavers following record-high fuel prices amid the war in Iran.

It comes after the president called for a ban ahead of a meeting with his Ukrainian counterpart on Tuesday. US Treasury Secretary Scott Bessent and Energy Secretary Chris Wright have both confirmed the administration is examining the proposal.

Diesel prices have reached record highs in both the US and Europe as the war in Ukraine and Iran cut exports from some of the world’s biggest products such as Russia and Saudi Arabia.

In Australia, which consumes the most diesel per capita, the price of diesel has risen by seven per cent to nearly $3 a litre, according to the federal government’s latest fuel data. Australia does not directly import diesel from the US, instead relying on refineries in the Asia-Pacific, such as South Korea, Japan and Singapore.

Treasurer Jim Chalmers said a ban would be “a very concerning development for the global economy”. The government also faces questions on whether it would reintroduce its fuel excise cut, which was ruled out by Deputy Prime Minister Richard Marles who said the government was not considering the policy.