The company tells him to charge more for a ticket if the customer uses a credit card

Praise be to Allah.

Firstly:

There is nothing wrong with you receiving payment for a ticket when a customer uses a credit card, whether the credit card is Islamically permissible or disallowed.

As for credit cards that are permissible and free of any reservations, the matter is clear.

As for those that are disallowed, that is because the sin of that which is haraam in them is borne by the bank and the customer, and the seller has nothing to do with that, because he is allowed to sell to those who borrow money with riba, and the sin of riba is borne by the one who commits such acts.

Secondly:

It is permissible for the bank to charge the vendor a fee in return for this service that it offers, which is making it easier to sell and get money from the customer; it is not permissible for the vendor to add this fee to the price of the item being sold.

The International Fiqh Council belonging to the Organisation of the Islamic Conference issued a statement on credit cards during its second session, held in Riyadh in the Kingdom of Saudi Arabia, 25 Jumaada al-Aakhirah – 1 Rajab 1421 AH (23-28 September 2000), in which it said concerning the use of credit cards and the fees charged:

It is permissible for the issuing bank to charge the vendor a fee for purchases that the customer makes, on condition that the vendor charges for credit card purchases the same price as he charges for cash sales.

End quote from Majallat Majma‘ al-Fiqh, vol. 3, p. 673

The reason why it is not allowed is: if the purchaser uses an uncovered credit card, he is essentially borrowing from the bank, and if he pays a fee to the vendor which goes to the bank, then effectively what it means is that he has borrowed from the bank and paid back the loan with something extra. Even though this was not stipulated in the credit card contract, it is something that the purchaser is still aware of, and when he borrows at the time of purchase, he borrows with a commitment to pay back what he borrowed plus something extra, and this looks like riba.

If the credit card is covered, then the bank is acting as a guarantor for the purchaser, and it is not permissible to charge a fee for being a guarantor.

Ibn al-Mundhir (may Allah have mercy on him) said: All of the scholars from whom we learned are unanimously agreed that acting as a guarantor in return for payment is not allowed and is not permissible.

End quote from al-Ishraaf ‘ala Madhaahib Ahl al-‘Ilm (6/230).

Ibn Qudaamah said in al-Mughni (6/441): If someone were to say, “Act as my guarantor and I will give you one thousand”, that is not permissible, because the guarantor is committed to paying off the debt (if the debtor does not pay up). Then if he ends up paying it, the one for whom he acted as guarantor now owes him, so it becomes like a loan; therefore if he takes a fee for it, it then becomes a loan that brings benefit, so it is not permissible. End quote.

Based on that, you have to stop asking for this additional amount from the purchaser, because it is causing him to do something haraam, and this is worse than helping in sin, because it is both helping him in sin and promoting it. Therefore that is not permissible, even if the company is telling you to do it.

And Allah knows best.