i never encountered something like that before.
and if you're really sent it you should have the transaction record right ? trx transaction / transaction ID ?
please provide it into your report and we may be can help you to find the solution.
so we can see everything in detail what is going on with your transaction.
there're a lot of problem happened in the exchanger lately,but i don't think they will scam you for just 290 or around that NXT.
it should be have a logical explanation about your problem,you might be accidentally sent it into wrong address ?
or typos ?

share the tx so we can see what is going on with your transaction