To get a receipt

Dear Sir/Madam,
I am Ms. ****** ****** and I bought some clothes (5 items) at Bershka Milaneo Stuttgart on 10th April.
I would like to change one of my clothes that I took a wrong size, M. My size is XS. The problem is that I have not received any receipt after I filled my email address at self-check out counter. On 10th April, I paid with card at self-checkout machine and to receive a receipt, I filled my email address. Later, I got an email from Bershka that I need to open an account, register first and download an application on my phone to get a receipt. Then, I registered an account when I was back home and when I received registration confirmation email, in that email, it was mentioned that I can download my proof of purchase after I completed registration. Unfortunately, although I finished doing registration process, I have not found any receipt in my Bershka account. The purchase history is still empty.
So, I went to Bershka store again on 25th April but they said they cannot do anything without the receipt. I told them I cannot do anything, too. They also tried to scan my QR code from my Bershka account to get a receipt, it did not work. So, they gave a customer service contact number. I called customer service phone number on 30th April but the staff said he cannot speak English and I can send an email. Then, I found a contact form from Bershka website.
Could you please help me how to get a receipt? I have attached my bank transaction, email screenshot and my Bershka account screenshots.
My contact number is +49 15235873593 and my email address is ******@gmail.com
Please do not hesitate to contact me if you have any questions.
I look forward to hearing from you. Thank you so much.
Best regards,
******