If you make partial payment you certainly will not be blocked immediately. There is time to resolve this. Make sure all of your previous invoices with them are paid in full.

Another option is to pop into a Salt shop. Preferably go with someone who is fluent in either French or German if you are not.

The Salt hotline will typically try to get rid of you to avoid the hassle and cost of the case and of refunding you, so over the phone it is unlikely you can resolve this.