A credit card company official told a court the facility to take card payments was withdrawn from an allegedly fraudulent website.
Sean Glynn said the high number of complaints against taxreturngateway led his company to terminate their agreement.
Businessmen Richard Hough, Michael Hughes, Jamie Wyatt, and Stephen Oliver are alleged to have made more than £5million in five months from the site, which offered to help users with their self-assessment tax returns.
Hundreds of people complained they were misled into believing they were dealing directly with Her Majesty's Revenue and Customs (HMRC), Teesside Crown Court heard.
Users thought their payments of up to £1,000 would be credited against their tax bill.
Mr Glynn, a credit analyst with First Data Merchant Services, told the jury his company enabled retailers to take credit and debit cards.
"We had a contract to do that with taxreturngateway," he said.
"The number of charge-backs, which is a request from a dissatisfied consumer for a refund, became a growing concern.
"In February 2014, we received 299 requests for charge-backs from customers of taxreturngateway.
"Customers were clearly concerned they were being misled.
"Following our own inquiry, we terminated the contract with taxreturngateway because of the growing number of complaints.
Mr Glynn said the directors of taxreturngateway, which was run from offices in Sunderland, later made refunds of approximately £340,000 to 700 people who had complained.
Jessica Dye, from the Advertising Standards Authority (ASA) told the court in 2013/14 it received an increasing number of complaints about websites offering 'government document' services.
"We called them copycat websites," she said. "Users were commonly misled into believing they were dealing directly with the government department.
"There was often lack of clarity over fees, with users paying more than if they used the government website.
"We received a number of complaints about taxreturngateway,"
Graham Trembath QC, defending Oliver, said the ASA had adjudicated on a number of complaints, and had given taxreturngateway a clean bill of health.
Ms Dye agreed that was the case, but said other complaints had been 'put on hold' while the ASA researched the general topic of copycat websites.
Wyatt, 27, and Hughes, 26, both of Peartree Rise, Seaton, Seaham, Oliver, 47, of The Folly, West Boldon, and Hough, 43, of Thorpe Waterville, Kettering, Northants, each deny conspiracy to defraud between June 2013 and June 2014.
Wyatt, Hughes, and Oliver deny a second charge of conspiring to defraud by denying consumers the right to cancel under distance selling regulations.
The trial is expected to take 10 weeks. Proceeding.