Wow. I'm so sorry you're dealing with this. I think you tried to handle the situation very gracefully, but that respect wasn't returned. Obviously you have to make the decision that's best for you and your family, but I have to point out that continuing to attend this church and following this pastor's edicts is teaching your children something about the value of breastfeeding, the value of mothers, and the value of infants, and it may not be the lesson you want them to learn.
You could provide him with further information about the reasons why pumping and bottlefeeding is not an acceptable suggestion, but he sounds like his mind is made up and he isn't open to hearing or receiving any wisdom you can impart. If his daughter has no issues with nursing her child secretly, then no other reasonable person could, right? Never mind that some women have fought like crazy to nurse their babies and struggle with supply, pumping, covering uncooperative babies. Those women are clearly not as worthy of receiving the teaching and love of Christ as a handful of perverts who get distracted and horny when they see a woman nursing her child. I know I'm ranting a bit, but I get furious when my faith is used as a misguided justification for hurting children and their mamas.
Verily I say unto you, Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me.