If you are transfusing him regularly and his Hg is above 10, you should not worry too much. Every child is different, they take a lot from parents genes in terms of structure and have different growth spurs and development charts. The development charts are general guidelines, ask your doctor if he is falling behind the standard baseline.
Do not worry about giving him iron rich food, the amount of iron they get from food is very small compared to transfusion induced iron. Of course you are not going to give him steak every day. You can introduce milk, meat, eggs, vegetable etc more frequently to your child without fear of iron. These foods contain lot of essential minerals other than iron which helps in child development.
As for audio test, 60% hearing loss (I think you mean 60db) this is moderate hearing impairment as per WHO charts, and will take some time to reverse. Please do not assume that there is no improvement, only authentic audio test will determine if the hearing loss has reversed. Please go for audio test.