Pair finance owes me money

I had many Aktenzeichen for one debt (wtf)

I paid EVERYTHING, I did it through their website, and then I summed all up and transferred the money to they account.

Still since couple of months they write to me that I still owe them money, when I send them confirmations of payment from my bank - nothing, I write to them they have to assign them MANUALLY - nothing.

The best part - they send me different numbers for each Aktenzeichen every time, sometimes less sometimes more.

Still I paid the amounts I got in one of the E-Mails and turned out, because they were sending like 10198448 E-Mails, I paid twice for some Aktenzeichen through their website, and overall they owe me over 150 Euro because I paid too much!

I dont know what to do it gives me so much stress.

I calculated everything many times and they do owe me money and the bank transfers went through

I am not a German citizen

Please help.