What to do if Yorkshire Bank are dragging their heals!

Greevo

We were told we have been successful in claiming PPI from Yorkshire Bank. We are owed over 10k. After 28 days we rang and said is there a problem, the bank said our signatures are not exactly matching. So I took time off work to go into the bank and sign again. After 20 days we rang the bank and they said they have not received the signatures at the PPI offices. We went into the bank to sign again but the girl on the counter said she definetly sent it and gave us a copy of the email. We rang the PPI office and they found it and said it would be paid within 28 days. They said it would be 2 payments one for 2.1k and one for 9k. They paid the smaller one out then said the other would follow. 20 days later we asked is there was a problem, they said we need to sign again. Could this all be because they said the offer was final and they did not have enough information on two other mortgages, but we have found the references! When we told them this they said we would have to start again and we said no, we we start when this payment is sorted? Any advice would be appreciated.