You know, it's hard to hear the present perfect sometimes, especially when it's contracted. That is, when have is reduced to 've and has reduced to 's:
I've finished it is pronounced I[f] finished it.
She's sent the letter is pronounced She[s] sent the letter.
Contracted have (spelled <'ve>, phonetically [f]) is not heard separately from <f> of finished, and contracted has (spelled <'s>, phonetically [s]) is not heard separately from <s> of sent. In those examples, contraction makes it appear as if present perfect verbs have merged to simple past verb.
All the best.