Basically, there is no way to "solve" the problem. Slippage is part of how the market works.
The Broker/s are not necessarily your enemy. You want to buy and sell currencies, they provide that service. The market does not necessarily have the price you want every time you want to transact. They are your intermediary with the market. Do no expect them to lose money while providing a service.
A good broker will give the best price available in that millisecond, a bad Broker will take advantage and slip you a bit further of you order price.
The Broker/s are not necessarily your enemy. You want to buy and sell currencies, they provide that service. The market does not necessarily have the price you want every time you want to transact. They are your intermediary with the market. Do no expect them to lose money while providing a service.
A good broker will give the best price available in that millisecond, a bad Broker will take advantage and slip you a bit further of you order price.