SL, you are wrong. Update.

2019-07-15

As it was suggested on reddit thread we’ve contacted Hallå konsument

Hallå konsument suggested to complain to ARN

You can turn to The National Board for Consumer Disputes (ARN). They are a public authority that functions roughly like a court. They try disputes between consumers and business operators. It usually takes about six months from the claim to a decision. ARN’s inquiry is free of charge.
For a claim to be tried it must be filed in writing and exceed certain value limitation. Read more about how to make a complaint and the value limitations on ARN:s webbsite:
https://www.arn.se/

2019-07-21

Now I decided to make SL answer how this situation could be avoided:

Dear Biljettkontroll,
thank you for your response.
I paid the fine but I think that your demand is illegal therefore we are proceeding with complaints to konsumentverket and ARN and if needed we’ll take the case to the court.
Also all conversation about the case is becoming public.
Therefore could you please explain what exactly we did wrong in our case so we or other travelers could avoid this situation in future?
Just to remind about the situation: we paid for two tickets on one card, biljettkontroll could see only one ticket(which seems to be a known problem), we provided proofs(reskassa historik) where it’s visible that two tickets were paid,
but still we have to pay the fine.
BR

No answer on this.

2019-07-24

We’ve made a complain to ARN

2019-08-09

Hmmm. Let’s remind SL about us. Sending separate message(not linked to the case):

Hello,
Could somebody answer on the last question in case 4013451705.
No answers since July 21st.
BR

No answer

2019-08-19

We received two emails now: one from ARN(today) another one from SL(on Friday).

Email from SL

Dear Julia,
We have decided to refund your previously issued fine. For this purpose we require the following information:
Clearing No:
Account No:
Bank:
Account holder’s name:
Account holder’s address:
There is a 50 kr administrative charge for refunds.

Answer from ARN

Hej,
AB Storstockholms lokaltrafik (SL) har tagit del av anmälan från Julia Urvantseva (Anmälaren).
Uppgörelse
SL gör upp med anmälaren då vidare utredning av ärendet visade att hon hade giltig biljett vid kontrolltillfället. Tilläggsavgiften avskrivs därför och beloppet återbetalas, via Riksbyggen, till anmälaren.
Med vänlig hälsning

Yay! Something!

We’ve send SL account details and also wrote that we believe that whatever fee should be paid it must be paid by SL, since whole situation is their fault from the very beginning.

2019-08-21

We’ve got 1514 SEK from SL today!

We’re going to answer to ARN now that after ARN contacted SL they returned much of the fine, but not the whole sum.