Samsung mobile india - Device damaged during repair

I have a Samsung Galaxy S** Ultra mobile(**GB/***GB Variant). I purchased this mobile phone online on April *,**** from Samsung India website. For the past month I have been facing a battery quick discharge issue. The battery of the mobile phone was draining faster than before. So my wife took the mobile to the nearest Samsung Service Centre to get it fixed. The Authorized Samsung Service Centre was B*X Service Solutions India Pvt. Ltd. The Service Centre told my wife to deposit the mobile phone at the service Centre so she deposited the mobile phone at the Service Centre in the morning on February **, ****. They told her that they will replace the battery and she can collect the mobile phone by evening. My Service number or Bill No. is **********. Around * PM when I checked the repair status of my mobile phone on Samsung website it was showing Repair Completed. So I called the Service Centre to collect my mobile phone. But I shocked to hear that they can not repair the phone as it was outside repaired. I told them the mobile phone was not repaired before and never opened. The only issue I faced before was that the S-pen was not detected in **** and I got the replacement of S-pen from the same service center. After that there was no issue with the mobile phone. I called Samsung Customer Care and they also directed the service team to repair the mobile phone as it was under warranty. But the technician refused to repair the mobile phone. Now they have opened the back panel(Battery Cover) of the phone and returned the mobile phone with the opened back panel. I requested the Service Centre to return my mobile phone as it was before but they refused, giving the excuse that they can not seal the phone once it opened. They also said that the display of the phone is not genuine. They also said that there is a dent on mobile and the dent on the bottom will be considered as damage to the mobile phone. (Even though it was just a minor paint off and does not affect the function of the mobile device in any way.) After so many arguments I took my mobile phone back from the Service Centre un-repaired and the back panel opened. Next day there was a vertical line appearing on the mobile phone screen temporarily and a horizontal line on top portion of display. I again contacted the Service Centre for a solution of this issue but they simply refused to service the mobile phone. I took the phone to another Service Centre and they refused to repair it as now the back panel is opened. They confirmed that all the parts are genuine including the mobile phone display. Now I have a mobile phone with a battery problem with the back panel opened and display with horizontal and temporary vertical line. I purchased this mobile phone directly from Samsung and paid full price. It was never opened or repaired anywhere else except the Samsung service Centre. I asked Service Centre team if there was visible physical damage to the mobile phone then why did the technician asked to deposit the phone even after first through inspection of the mobile phone. They opened the mobile phone and did not inform me about the damage. I checked the status of my repair on Samsung support website as it showed that the repair was completed and ready to deliver to the customer. Then I called the Service Centre in the evening to collect the mobile phone and only then they told me it was "outside repair". But by then they opened the mobile without informing me. I asked them about the CCTV footage or video recording of that day but they refused saying they don't keep recordings for that long. Because I do not trust the technician there and it might have happened that it was some mistake of the technician while repairing the mobile and to hide that mistake they are putting all the blame on the customer. I put the tempered glass on the mobile phone to protect the display from scratches which is quite common. If my mobile phone is under warranty then why should I go to any other shop instead of Samsung service Centre. So it means I purchased a faulty phone from Samsung and never noticed anything wrong as I am no expert in these things. Or it may have happened that the technician at the Service Centre did something wrong and is now giving other excuses to hide his mistake as there was nothing wrong like this with the mobile phone when we deposited the mobile phone at Service Centre. I sent email to Samsung India support and called on their many times. But they did not give any solution giving various excuses. They escaped from their duties of providing good service to the customer. It is really humiliating and mental torture for me as I paid for a premium product and got this kind of service.