New inground pool owners...vinyl liner help!

Im new to the forum and Im not sure if this is the right place to post this or not, but here is the problem :)

My husband and I just moved into a house with an inground saltwater pool about a month ago (the previous owner says its between 25k-30k gallons) - we've never owned a pool before so everything is new to us. The previous owner said it was very low maintenance (haha! what a joke) and all we had to do was add pool salt to the skimmer when the Aqua Rite read below 2000. It has a vinyl liner (that is about 5-6 years old) that had got some water behind it, which caused the liner to come off the track and bunch up on the bottom and float out on the sides. According to the previous owner, his kids were jumping off the sides of the pool and it happened a few weeks before we moved in.

We contacted the pool guy who had been servicing the pool and he told us to drain the pool down to the deep end and leave about 1/2 an inch in the shallow end 2 Sundays ago (July 13th) and it was supposed to be fixed that following Monday (July 14th). However the pool guy's "guys" didnt show up until that Friday (July 18th) and by then the liner had started coming off all around the pool. They fixed it Friday and said that they suctioned some water out from behind the liner and that the other water would "disappear" and then put the liner back in the track. I questioned them about any holes/rips and they said everything looked great.

We were told to start filling it up again...so we did. As we filled it on Friday/Saturday the liner came out of the track again - I called the pool guy and he said, "no big deal", when he came to get the sand bags later that day he would fix it. They didnt show up until Tuesday to get the sand bags and then tucked the liner back in. Of course, because of lack of filtering, the water was nasty green so we were told as soon as the pool was full on Saturday to put 1 bag of shock in the skimmer and run the pump and start adding the salt back in. We did just that and nothing happened other than it just turning "greener."

So we decided to take some water to be tested and ended up spending $300.00 a few days ago on chemicals - stabilizer, algaecide, calcium, more shock, and Super blue. Over the past few days we have been diligently working on getting the water to look great again and this morning it looks clear and beautiful and tests great. However - the liner is bubbling up again and it seems water behind it ....again - worse than it did before it was fixed the first time and the liner has come out of the track again and there are about 3 times as many wrinkles on the bottom as before. The liner was fixed less than a week ago. We have a Polaris that runs, but gets hung up on the wrinkles so we currently dont have it running.

Im slightly frustrated at the fact that we just spent so much money on chemicals and i feel like i may have to drain the pool again to fix this and these past 2 weeks we have been battling this we have had summer visitation with my husbands kids from a previous marriage - so you can imagine their disappointment when they came over and couldn't swim.

The guy we are using is the one that put the liner in for the past owner but he doesnt have very good communication with us about what is going on, when he will come, and just says everything is "not a big deal and its all super easy." We have only been in the pool 1 time since it was "fixed".

Is this something that happens often in vinyl lined pools? Is it an easy fix for the homeowner or do we need to get it professionally fixed everytime? Is there a way to prevent it? Is there a way to convert this pool to something more durable so that we aren't having to deal with this every year? Do we need to replace the liner?

Any help would be SO much appreciated and thank you so much in advance! :)