Dumpster question

We ordered a dumbster to use for renovation. The person on the phone sold the jib for $395. That is what we agreed on. He ran the card for $400. I didn't say anything to that. We were happy to get it at that price. We talked that it covered 2 weeks pick up. The dumbster arrives and then driver said keep it for a month. Then we get an email from the company wanting us to sign a contract. We couldn't pull it up on our phone and they didn't call back. We fill the dumbster. We call in a month and they send over this contract to sign. My girlfriend typed my name and emailed it back. We immediately get an email. It says we owe for having it too long and they need so much on a credit card if it is over 1 ton. We did not agree with this. They won't pick up unless. They have threatened to dump the trash in our yard. What is my obligation?