As a former Chief Flight Instructor this is unacceptable. Sounds like poor oversight and supervision which is not surprising with the the state flight training is in these days.
I councell aspiring pilots to educate themselves on the flight training standards. Know where you should be and if you don't meet those targets you better start asking why. If you let the Flight Training Unit spoon feed you, you will be taken advantage of and won't be able to recognize incompetence which is so rampant in the Flight Training Industry. Educating yourself is good practice if you plan on moving on and making it a career. Industry expects you to learn on your own these days with CBT being the norm. Look at it this way at $240/hour, the going rate for dual instruction, you've wasted nearly $8500. Thats a huge chunk of change. Gone. Wasted. Sure its hours in the logbook, but they are dual. Next to worthless in terms of licensing, and employment if you plan on taking it further. Anytime you invest in something, it is wise to do your education and research beforehand to get a good return on investment.
At 50 hours with incomplete information I can only assume that either you are completely incompetent and unable to learn, the flight training unit is taking advantage of you, or you're receiving incompetent instruction. I lean towards the second one, as the FTU's can recognize a sucker a mile away. If you'd educated yourself on the process and expectations, you should have been asking questions of why you haven't soloed after 15 hours, but hey it's your money to waste. 50 hours used to be the average to obtain a PPL back in my CFI days for a busy, controlled airport.
It's time to take a hard honest look at why you haven't soloed yet. Look at yourself and see if you're missing something. If not, back it up with the flight training standards. Otherwise take your business elsewhere, but do your research this time. When I was CFI I picked up a few people from other schools in your situation. The majority of them I was able to solo them the day they showed up. The rest it involved a core competency that wasn't enforced during BFM. I only had 1 person show up that just shouldn't be flying airplanes, and it was mostly due to fatigue from them showing up after the night shift.
Instructors fail to remember that students are not required to be at PPL flight test standards for the solo. They only have to be safe. They can bounce, land long, not hold altitude perfectly, etc, etc. Flying is easy. Flying precisely takes practice. The goal is to get to flight test standards at the end of training, not at the beginning. If you haven't read the Flight Examiners Guide, you should. Large deviations outside the Flight Test Guide are allowed as long as they are corrected and the overall goal of the exercise is met. They just have to manage those errors properly. Much of the time you can tell they are ready when the learning curve plateau's. Continued instruction would be just flogging a dead horse, and can make things worse. You will be wasting the students money and possibly lose them to another instructor or school.
Sometimes you just gotta let 'em go. You should be nervous when you send them up. It's time for them to learn on their own the hard way. Your job was to give them threat and error manage strategies to come out of it safely. If they truly are not ready, then it's time for the CFI. Continued instruction could actually hinder their progress.
