LONDON (Reuters) - Former RSA Insurance Group (>> RSA Insurance Group plc) Chief Executive Andy Haste was on Monday appointed chairman of Wonga, tasked with pushing through changes at Britain's biggest payday lender which has come under fire for its treatment of customers.

Wonga and other short-term lenders have come under increasing scrutiny from politicians, regulators and even the Church of England over their high levels of interest rates, which can cause hardship for customers.

Wonga was ordered to pay 2.6 million pounds in compensation to 45,000 customers last month after sending them bogus letters from non-existent law firms that threatened legal action.

U.S. payday lender Dollar Financial, which trades in Britain as The Money Shop, on Monday agreed to refund 700,000 pounds in interest and default charges to customers who were loaned too much money.

Haste, who led RSA for eight years until 2011 and is senior independent director at ITV (>> ITV plc), said the payday loan industry was going through significant change and that Wonga "will change with it in order to have a sustainable future."

"My challenge is to lead that process of change at Wonga to ensure that the business operates responsibly while providing an effective and reliable service for our customers," he said.

The company's former chief executive, Niall Wass, quit in May, seven months after taking on the role from the Errol Damelin. Damelin, who co-founded the firm in 2006, quit as chairman of the company in June.

Wonga is currently charging an annual interest rate of 5,853 percent, according to its website. Wonga says that its loans are not meant to be taken out for that long so customers would not, in practise, pay that level of interest.

Britain's Financial Conduct Authority, which took over regulation of the sector in April, is considering imposing a cap on the levels of interest payday lenders can charge.

(Reporting by Steve Slater; Editing by Matt Scuffham and Pravin Char)

Stocks treated in this article : ITV plc, RSA Insurance Group plc