NHS Test and Trace chiefs suspended operations at Wolverhampton-based Immensa Health Clinic Ltd in October last year over fears an estimated 43,000 people had been given incorrect negative PCR results.
The firm's sister company, Dante Labs, has now been investigated by the Competition & Markets Authority (CMA).
The probe, launched in September last year, was in relation to "fit-to-fly" travel tests being offered by Dante Labs on its website, after claims the company failed to provide kits and results quickly enough, or at all, failed to respond to complaints and refused to issue refunds.
Companies House records show Andrea Riposati is the chief executive of Dante Labs, and also holds the same position for Immensa Health Clinic, which was formed in May 2020.
In October 2021 it was reported that Immensa had continued to process results for international travellers who bought tests through its sister company after the NHS intervention.
The CMA has now announced thousands of customers had received their money back from Dante Labs, and the firm had committed to pay any outstanding refunds.
The competition regulator has secured formal commitments, known as undertakings, from the firm – which will complete its review of complaints from the summer and ensure people have received refunds if they tried to exercise their cancellations rights or if their test kits or results were provided late.
The testing firm must complete any outstanding refunds within 21 days and must strengthen the protections for customers in its terms and conditions, improve customer service and provide clearer product information.
The company has pledged to advertise clear information about the services it provides and include the time-frames expected for test results to be delivered and ensure customers know their rights for cancellations and refunds.
It will also maintain a proper customer service system, which includes responding to complaints and queries in a helpful and timely way, and provide the CMA with an update report in three months on its progress implementing all the changes.
Andrea Coscelli, Chief Executive at the CMA, said: "No PCR testing firm is exempt from the rules and our action to secure these refunds and other changes shows that we will not tolerate poor business practices.
"While travel rules to the UK may have changed, those people who still require PCR tests to travel abroad shouldn’t have to waste money on late results or tests that don’t arrive.
"It is crucial that all PCR providers treat people fairly, being clear on price and timings and providing refunds where they are due."
The investigation into Dante Labs forms part of a wider action from the CMA to protect people buying PCR tests, with an open letter issued last year outlining how providers should comply with consumer law.
The regulatory body also sent letters to 25 PCR test providers, warning them to review their terms and conditions – and other practices – or risk enforcement action, leading to changes being secured from major PCR test provider Randox.
Meanwhile the CMA has another formal investigation into another test provider, Expert Medicals, and are expected to provide an update in "due course".