You could take action if either of them are in breach of contact or have in any way been negligent. However my concern would be that court action would take longer than the contract even if there have been delays. Have your solicitor contact them and find out exactly what the issue is and when it will be resolved. Your solicitor can threaten a case for damages for inconvenience.
Yes you can, on the basis that you need a lift and thus are being treated less favourably than someone who does not have a disability.