Its their fault, they monitored the job they did the job, they did not
give you instructions or orders to follow that you failed on. I dont
know pools but if paint , concrete , plaster, mortar, welds , etc dont
bond you remove all loose product and redo the job.
If they dont jump to fix it or agree in writing to a agreement tell
them you will file small claim for full cost. here it costs 35$ and
takes 5 minutes, That will get them a movin.
It possibly was bad surface prep. Either way get an agreement today or
file, tell them you will drop claim if its fixed.