SportsDirect.com review: Formal complaint regarding unusable credit note and poor in-store service

I am writing to make a formal complaint regarding a credit note issued to me following a return in 2024.
I initially attempted to use the credit note online but was unable to do so. I contacted your customer service team and was advised that the credit note could be used only in a Sports Direct store - in store purchase.
However, when I visited the store in Cambridge - in Grand Arcade Shopping Centre, the manager refused to accept it. I contacted customer services again and was reassured that the credit note was valid and should be accepted in store.
Following further contact with customer services, the same store manager eventually allowed me to use part of the credit note. The remaining balance was returned to me, but the manager failed to provide or add the required PIN. As a result, I am still unable to use the outstanding balance. 

At the same occasion the manager made comments on my ability to keep the credit note safe, also confronted me him “being right” when he suggested that “I lost the original”-despite the fact your customer service confirmed in writing that my credit note is valid. He also made criticism comments for me returning that previous item as “he never returned anything in his life”. The whole process took long and made me feel very uncomfortable.
his matter has caused considerable inconvenience and frustration. I have followed the advice provided by your customer service team, yet I have repeatedly experienced difficulties when attempting to use a valid credit note.
I request that Sports Direct urgently:
Provide a valid PIN or issue a replacement credit note that can be used without further difficulty.
Investigate the way this matter was handled by the store manager.
Provide an explanation and appropriate resolution for the inconvenience caused.
Please treat this as a formal complaint and respond within 14 days. I can provide copies of the credit note, receipts, and details of my previous communications with customer services if required.
I look forward to receiving your prompt response and a satisfactory resolution.
Credit note numbers: [protected] and [protected]