We had a 30 day evisa for Vietnam and planned to cross to Laos through Taichung/Dien Bien. (Northwest).
We got our Laos visa through the Laos embassy in Hanoi as this allows you to cross any border you want and you can activate it within 2 months. (Valid for 30 days, not exceeding the expiry date of the 2 months).
Anyway, we overstayed 2 days in Vietnam because on the day we wanted to cross I got food poisoning and was not able at all to move anywhere. It says online on various websites that you just pay 25 USD and be done with it. - not true!!!
Long story short, we were sent back to Hanoi after a struggling journey to Dien Bien, to go to the immigration office to pay the fee as they have no authority to deal with penalties at the land borders. Keep that in mind if you're overstaying in Vietnam! You always have to pay in Hanoi!
Edit!!! The processing time is 3-5 working days so you have to book another few nights accommodation in Hanoi before you are allowed to leave the country... Madness. I will keep editing as we progress through the situation.
Edit & final results (detailed procedure):
It all happened on a Friday so we had to go all the way back to Hanoi (10 hours) and of course the immigration office was closed over the weekend so we went there first thing Monday morning.
You have to pull a number and wait to be called but we noticed that a lot of people just skip the queue and since our matter was quite urgent we did the same and were really able to speak to somebody within 10 mins or so.
We had to give them our passports and were told it takes a week to process everything and we should be able to pick them up again on Thursday but have to book a flight to leave the country on Friday.
Of course we were very unsure of actually getting the passports back by then and then having to cancel our flights without any money back. He basically said not his problem but told us to do it. It's communism so the rules are the rules...
We were told to come back on Thursday 4pm but thankfully my gf decided to go there at 3pm. Good job because they actually close at 4pm so he was already fooling us!
When we arrived we had to pull a number again but skipped queue again as well and had to pay a fee of 25 USD each as far as I remember. I thought that was it but it was just the admin fee. We were then given an invoice of over 100 USD each (cent remember the exact amount but was over 100 USD) which needed to be paid at the bank that was 1km away! Not even at the immigration office you could pay. We were rushing to the bank as they were all closing at 4pm. When we got there we wanted to pay by card but then were told they only accept cash. I was like, ok then we withdraw money. Their answer was they don't have any ATMs.
We couldn't believe what a shit show this was and had to walk across the street to the bank in order to withdraw cash before going back to the other bank and finally paying the invoice. Upon payment we got a receipt that we handed over at the immigration office again.
We were then told to come back tomorrow for the passport. This was the moment where I was raging as they were really just pulling the piss with foreigners. Thankfully I noted the batch number of the uniform of the guy that was looking after our case the previous Monday so I said I want to talk to him. Eventually he came but also said tomorrow which was not acceptable since we were told to book a flight and we will get the passport.
They had a chit chat, looking at us, laughing at us clearly, making us wait even longer and then eventually at exactly 4pm were were handed the passports that were sitting right behind him all along in the shelf!
It is an absolute joke dealing with these offices as there is a huge sense of discrimination and muscle power.
Bottom line, done overstay your visa. If you do for medical reasons, get a certificate from a hospital!