i paid twice

i had a fee of 120€, i contacted the customer service by email, got an invoice, i paid it, i was told if i sent a screenshot it would be resolved quicker, i sent a screenshot, i got an email response telling me that the o2 received the money and my phone number was therefore unblocked. a week or so after that i was told to pay again after they blocked my number again, then i called the o2 english customer service, they told me that i shouldve put an invoice number (which i admit is my fault), they told me i have to know german to speak to the finance department, i cant speak german nor do i know anyone that can. i went back to the confirmation email (it was a thread of emails) and i emailed them about it, they read it, told me that i only paid once, though i had multiple evidence that i paid twice, then when i told them no i got paid twice and showed photos, my email got ignored for 2 weeks, after that i emailed again, no response, i emailed again and again, till i finally got told that my email is “being processed”, its been 2 months and my email still has no response, i emailed them again since then, still no response. this is unacceptable in every aspect, i got charged twice, and the customer service doesnt care. i paid 240€ instead of 120€.