English is confusing in some cases

I believe that English pronunciation is confusing, I was listening to music, specifically exactly Demi Lovato and Avril Lavigne. Demi Lovato pronounces the letter D as an R and the letter T as an R also. For example, in the phrase "I don't"... shes she pronounces the D of Don't like an R and I hear "I ront" as a spanish "ere", also in the line/verse prase "but a" I hear "bara." how can it be if the last end T sounds like a soft R, but Avril Lavigne pronounces Don't and But a with corresponding correspondings sounds ("don't" don't and "but a" as but a)

I don't know which is isn't correct. My current teacher is from New York, he pronouns pronounces words like Demi Lovato but my last teacher who was from Canada, pronounces words like as Avril Lavigne; the R and D.

English is confusing in some cases

I believe that English pronunciation is confusing, I was listening to music, exactly Demi Lovato and Avril Lavigne, Demi Lovato pronounces the letter D as  R and the letter T as  R also. for example in the phrase "I don't"... she pronounces D of Dont like R and I hear "I ront" as a spanish "ere", also in the phrase "but a" I hear "bara" how if the end T sounds like a soft R, but Avril Lavigne pronounces Don't and But a with corresponding sounds ("don't" don't and "but a" as but a)
 
I don't know it isn't correct. My current teacher is from New York, He pronounces like Demi Lovato but my last teacher who was from canada, pronounces as Avril Lavigne the R and D.