One plus - Unfair trade practice by a mobile centre

This is regarding my recent experience at the One Plus service centre located at Mobile Doctor, Ground Floor, #***, ** Feet Rd, *th Block, Bengaluru, Karnataka ******. The incident took place on Sunday, September **th ****, when I visited the service centre to replace the shattered back glass of my One Plus * phone.
Upon arriving at the service centre at **:** noon, I inquired about the availability of the back glass replacement. The service representatives assured me that they had the replacement part in blue colour and claimed that they exclusively used original parts, as they were an authorized service provider. They provided me with a quote of Rs. **** for the replacement, which I agreed to.
The service centre staff estimated that the replacement would take approximately * hours to complete. I proceeded with the replacement and inquired about a physical bill, as they had previously mentioned a *-month notice period. However, they informed me that they did not provide hardcopy bills and assured me that they would send the bill via WhatsApp within half an hour. With this understanding, I left the service centre.
However, I never received the bill on WhatsApp as promised. Upon returning home, I removed the rubber bands that had been placed around the phone to secure the back glass, as instructed by the service centre staff. Unfortunately, the back cover began to detach shortly after I removed the rubber bands.
Concerned about the quality of the replacement, I visited an exclusive One Plus service centre on Monday, September **th, for a professional inspection. To my dismay, the technicians at this service centre determined that the back glass replacement was not authentic, which explained the poor adhesion.
Subsequently, I returned to the original service centre to address the issue. I encountered the manager, Mr. Sayyed, who vehemently denied any wrongdoing and engaged in argumentative behaviour. Despite my persistent requests, the service centre continued to withhold the bill and provided excuses for not sending it promptly.
To rectify the situation, Mr. Sayyed reluctantly agreed to replace the back glass and requested my home address. He assured me that a technician would visit my residence on Wednesday, September **th, to complete the replacement. However as of today, Thursday, September **th no one has visited and he has not been picking up my calls.
I have attached the note provided by Mr. Sayyed for your reference. I have also attached the online payment I had made to their staff.
I am deeply dissatisfied with the lack of professionalism and transparency displayed by this One Plus service centre. I believe I have been subjected to unethical practices, including the use of non-original replacement parts and the failure to provide a valid bill. This has resulted in additional inconvenience and expenses for me.