US Trademark application drags after 7 months and $1700

We applied for US trademark for our domain name(non generic term) through a trade mark agent in our city. Initially we were told it would cost around $1500. But we already spent more than that and the process not finished yet.

Everytime they send an invoice for various reasons it feels like we made a mistake by get into this. I was wondering if this is the case usually and how we can get it over with?