iTunes updating pause problems

I live in a country which the internet speed is not good and I want to update my phone via iTunes and it is nearly 9GB. I needed to pause my download but when I did and tried to resume it it started the download at 0KB. I am absolutely ****** because of my bad connection I had to redownload it 5 TIMES! and it's not done.

I nearly spend 25GB on literal nothing, It costed me 8 dollars worth of net in my country for nothing.

I have tested all the methods such as restarting pc and reinstalling iTunes but it didn't work.

Can somebody please help me?