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

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.