The damage in the tank wall mayb e from when the pipe snapped off. My guess is that somewhere along the line, a cleaner's scraping spade hit the pipe, but it was partly rusted already.
You could try showing the photos to a different septic tank maintenance company for an opinion and an estimate to fix and clean out the hard sludge. The sludge is probably dirt that washed into the hole in the tank wall.
To find the pipe coming from the house, dig straight from the tank wall a few feet. If it isn't there and the pipe is metal, perhaps use a metal detector, starting where the pipe leaves the house. You can also rent a locator, such as those that Miss Dig people use. If you know an electrician, she may have one. And, there are companies who will locate it for a fee.
If the pipe is plastic and you can't find it, dump some food coloring or dye in a drain inside & run water. If it does not show up near the tank hole, the pipe is broken farther back. Try using a blow-out bag (photo below) in a pipe and send hot water through it. You may see steam coming up from the dirt if the pipe isn't deep. Or try compressed air in the bag. You may see bubbles coming up through the dirt. That will be where the pipe broke.
Worst Case: Dig outside the house where the pipe exits the building and continue to the tank. Replace the whole line. But, how deep is it? How far is the tank away? Are you hand digging clay or sand? It might be a big project to expose the pipe, but replacing will be quick and easy.
If it takes an excavator to get the lid off, perhaps you can have a lighter one made from aluminum tread plate. Or, was the guy too lazy to pry & drag?
I think it's really, really important to make sure the building sewer gets into the tank. This is primarily for health reasons.
Paul
PS: That water in your photos is probably loaded with pathogens from the sewage leak. The white foam is a clue. Handle it with care.
