Child contact advice please?

I was ill in 2007 and I asked my ex husband to have my 2 kids for a week but he moved 100 miles saying id abandoned them and it took 3 years for battling legal aid and courts to see them again. Ive had contact every 4 weeks for a few hours due to the distance. Last week I asked could I have them every school holidays for a week at a time instead to give us quality time together and because financially I cant afford to go every 4 weeks. I dont drive so have to go by train. Ive booked an hotel where they live in july for a few days and want the children to stay with me. My ex and girlfriend say ive broken the original court order and they have stopped contact and they are getting me charged with contempt of court and to be put in prison. Ive never heard such nonsense but my ex says the order says it. His girlfriend has been texting nasty messages too telling me to disappear and I cant see the children again. They are 9 and 11. Im really upset because the children will be upset. They are being unreasonable and I dont know my legal rights. Thanks in advance