HR Departments of airlines are the most incompetent departments of all. The lowcost operators probably have just pushed the job of recruitment onto someone's plate. That someone neither cares nor is probably capable.
Seeing as you most likely have to pay for your endorsement these days, don't worry about them and move onto another operator.
That sort of thing happened to me with a company earlier in my career and funnily enough, they wrote to me a few years later.It was like it was an instantaneous response to a first application and they were expecting me to be checking the mail twice a day for their letter.
You can guess the response they got from me. Undeterred, they kept writting back every 6 mths or so for quite a while.
Still scrapping to find pilots now but,tough!
Good luck and don't let the bast-rds grind you down.