Battery capacity less than is specified

I bought a brand-new Galaxy S21 from Cellucity paid cash and not on contract. From the first day I noticed that the battery when charged to 100% looses 2% very quickly. I noticed the next day after a full charge and only using for 5 minutes I used 2% without heavy use only checking email, SMS, and WhatsApp. On the 3rd day after charging to 100% and without even using the phone it lost 2% in 20 minutes. On the 4th day I did a similar test with the same result. I also experienced random overheating without even using task intensive applications. I also experienced on 2 occasions during load shedding of having no LTE connection. On the 1st occasion it was late at night, so I did not really take notice of it and just went to sleep but on the 2nd occasion it was during the day. Restarted and still no signal. I then switched off removed sim and placed sim in my old phone and had no problem with signal. Placed sim again in S21 and still no signal, at that stage I was getting frustrated and decided to switch off phone for a couple of minutes and see what happens, luckily after that I got LTE signal, this could have been a random glitch but still I expected better from Samsung. I informed Cellucity on the 5th day about these issues and wanted to book it in as OBF, but the manager told me I must first do latest update, which I already did when I got the phone on the 4th of February, then he recommended I use it another 2 days to see if it is still the same. Phone was sent for assessment and came back as no fault; I asked the manager what was done, and he said they tested and found no fault. I setup the phone when I got it and after setting up and installation battery was low, I charged it fully to 100% and experienced the same problem of first 2% draining quickly. The manager told me it is most probably software, which I disagree with and told him that according to the specification the battery capacity is lower and that is definitely hardware and not software. I have been an avid support of Samsung my whole house is full of Samsung fridge, washing machine, tablet, watch, old laptop (which I still enjoy using), various phones (that I had and some I’m still using) and microwave but this experience with Samsung will put me off completely. I was deciding between this S21 and the new iPhone and decided on the S21 but am regretting it now. This experience and if Samsung don’t correct it will cause me to be anti-Samsung and I will stop promoting and coming to Samsung defense with people. So from the time I got phone it has been longer at Samsung than what I had it and already lost ½ month of the guarantee so for me to send it in again and loose another ½ month is unacceptable if the technician did a proper job and tested like I said then he would have picked up the battery issue when 100% charged and going to 98% quickly. Which is unacceptable and not as advertised 4000mAh, I also used an app called Accubattery which gave the battery capacity at 3780mAh so this clearly show that the battery capacity is more than 5% less than specification.