Mee-yah is how I would pronounce it.
Change it if you want, but Mia (Mee-yah) is a nice name.
FWIW, me and DH knew we were having a girl (from about 5 months into the pregnancy) with our first born, and decided on a certain name, (let's pretend it's Olivia.)
I regularly spoke to her when she was in the womb, and spoke her name (Olivia,) over and over. When she was born, DH started saying he liked a different name, (let's say Samantha,) and said she 'looks like a Samantha.' I was like 'WTF?' 
After she was born, DH kept calling her Sammy and telling people we were going to call her Samantha. I asked him where the fuck he'd got that name from. He had never mentioned it til the day she was born! I did not want our daughter being called that name. We'd decided on Olivia 4 months back, and I loved the name.
I stood my ground and dug my heels in, and when we went to register her at the register office, I said OLIVIA very firmly. DH said 'no Samantha then?' I said 'NO!' Glad I dug my heels in.
I am sorry you have been bullied/coerced/railroaded into giving your daughter a name you didn't want. Change it if you really want to. Cite the reason (to your DH) as 'people cannot pronounce it right!'