Rebuild old PHP site on NEW PHP, mobile friendly platform w/new features.

I have an old php site that is currently active online with about 50,000 monthly visitors, and thousands of registered users. I need it rebuilt on a new mobile-friendly, responsive framework, and all the users and data from the old mysql database to be moved to the new site. Front end is already finished, so I just need the backend done and integrated with current front end code. I need someone with expertise and determination who can succeed where others have failed, and who won't give up until the job is done. History: It took 7 years, and about as many coders, each building on top of the last, to finally get it done to the point where it was ready for 'public use'. Since it went 'live' back in 2010 I've been trying to get it rebuilt, since by then it was already outdated. I've been trying now for more than 7 years to get my site rebuilt without success. Now the original core php framework it was built on is more than 14 years old, and I'm desperate to find someone who can finally get the rebuild done. I've started over 6 times, with 6 different providers, who each promised me they could do it, but none of whom delivered. Every one of them wanted to start over from scratch, rather than finish work the previous person left undone. First 3 attempts were on a Drupal platform. 4th on Wordpress. 5th on last version of Laravel. 6th on new version of Laravel. 6th attempt is with same person who worked on 5th version, who said he could finish what another provider started, but after a year of working on it then claimed he would be able to get it done a lot faster and better if he could start over again from scratch, rather than trying to fix the last guys coding problems. So, between the last two guys, we spent nearly 3 years trying to finish rebuild number 5, and #6 has been a work in progress for about 6 months now. However, I had the front end built by someone else, so the front end is finished, and only the backend needs to be done, and since current guy already had a big head start he promised he could get the job done very quickly if he was allowed to start over. After 6 months with nothing to show, I am about to give up hope that he can do it, since he has missed every deadline he's given me/himself, or that I've given him. Because I am about to give up on the current work in progress, I'm just looking to see if there is someone who can finally get the rebuild of my site done. As mentioned, the front end work is finished. But the site is complex and there is a lot of data and thousands of users to be transferred. My site is non-profit and free for everyone, and does not bring an income, so I don't have deep pockets. And I am just one person, not a business or a corporation, so the costs are coming out of my own savings, which are nearly depleted. If the site is rebuilt with the additional income-producing features I want, then it will potentially raise funds in the future, and I can then afford to provide ongoing work for whoever I hire, if they get the job done. But for now I need someone with serious expertise and a great track record who is also affordable, and not afraid to tackle a problem that others have been unable to solve.