HELP!!! Plumber is overcharging me!

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I own a rental property in Harrisburg, PA. I live an hour away. A month ago, there was a sewer backup in my basement. I called a local plumber and my bill came to $8,000. I asked for a detailed report of the work that was done, and here is a report from the plumber (attached). My concern is how do I know that the rocks and metal that the sewer auger could not clear were really cleared/removed from the pipe? I have doubts about this because,  all plumbing was useable after I got charged and paid $3,130. The plumber went on to suggest that in order to avoid problems in the future they needed to cut out the pipe remove the rocks the sewer auger could not break and replace the pipe and this was going to cost me $4,350. He said if that is not done its only a matter of time (months/a year) before the problem starts again. I agreed to all this because I was really worried that the problem may surface again in the near future and it will end up costing me more money according to the plumber. I feel like I was overcharged. I have not paid the $4,350 yet. Is there a way to verify the job was done? Was he not supposed to take pictures and send to me to show me the rocks were indeed removed? Not sure if this is even possible. I did question the hours and he did say the hours included on site and off site hours needed to pick up the materials also waste needed to hauled away and disposed of. Not sure if that's how plumbers charge for their services, I know nothing about plumbing. I have attached some of the pictures from the plumber and of the waste they removed and also the invoices for $1830, $880 and $510 which I have already paid. I would appreciate any help/suggestions that can help me deal with this situation. Thank you all in advance!