Yes, it is normal for a broker to charge negative swap as long it is indicated on the agreement. Read the agreement of your broker, maybe you just missed some part of it.

In foreign exchange markets a swap can generally mean two totally different things. For example, a foreign exchange swap or interest rate swap is a type of transaction involving an agreed upon exchange of an amount of two different currencies - each at a specific interest rate that accrues over time, whereas a swap charge refers to an interest rate differential between two currencies and is applied to spot forex trades which are carried past intraday (held overnight).