about the transport service which you should provide without delay on requestfor the transport service which needs to be provided by you on request without any delay...
The next bit is unclear- you talk of an agreement and a contract. Are they two different things? If not, then say ...on request, as agreed in the contract. or as agreed.
The transport service has not been provided promptly and deliveries are always (always or frequently??) delayed without any satisfactory explanation.
The last bit depends on what sort of agreement you had with them.