IIn November I purchased four One Direction concert tickets and travel from Cavendish Travel paying £340 total. They were a Christmas present for my daughter. Soon after, it emerged Cavendish Travel had gone into liquidation. Its website said no tickets would be issued. It advised customers to contact their bank.

As I had paid using my Santander credit card, I assumed this would be a straightforward section 75 claim. I filled in the forms, sent copies of correspondence, etc and waited for my money to be repaid. However, the bank has turned down my claim on the basis there was a "break" between me and the concert promoter.

I feel I have a legitimate claim and contacted Santander several times, but am getting nowhere. CJ, Clockheaton, W Yorks

Section 75 of the consumer credit act makes the card provider "jointly and severally liable" for any breach of contract, which is why we always advise readers to pay for expensive items using a credit card. In theory, it is there to protect against incidents such as this.

To gain the protection, the item or service you bought must have cost over £100 (and not more than £30,000). Section 75 gives you the same rights against the card company as you have against the retailer in the event of a problem.

The protection, though, does not cover all eventualities – and Santander seemed to be arguing that, because the agent, rather than the concert promoter, had gone bust, the bank wasn't liable – which is a debatable stance.

Consumer group Which?'s webpage says: "It's not unusual for a business taking payment to be acting as an agent for the supplier, for example buying a flight through a travel agent or insurance through an insurance broker. In these circumstances section 75 should still apply and you should be able to claim against the credit card provider."

However, it goes on to say that if you bought two items that together cost more than £100, but each cost less than £100, the card company "wouldn't usually be liable" – as in your case.

Section 75 does not apply if you use a third-party payment firm, such as Paypal, either. To get the best cover you need to book direct with the provider of the goods or service, and pay them directly using the card.

Happily, Santander has had a rethink and offered you a full refund as a gesture of goodwill.

Addressing the issue …

Two weeks ago we featured the case of MH, Burton upon Trent, who had received a solicitor's letter saying they had been instructed by Santander to begin repossession proceedings. The bank said it had sent him 50 letters about one missed payment – letters, he had said, he had not received.

We asked if any other readers had had a similar experience. Several of you said that letters from both the mortgage and banking departments had simply not arrived. Non-Santander customers also reported getting post from Santander addressed to other people.

CB's letter was typical. "I had a number of letters go astray. Santander has only ever held my current address, and has confirmed this. Despite that, letters continued to go astray. They received no returned mail. I do, however, have two letters which have the wrong address on them."

We welcome letters but cannot answer individually. Email us at consumer.champions@theguardian.com or write to Consumer Champions, Money, the Guardian, 90 York Way, London N1 9GU. Please include a daytime phone number