TOPIC: procurement contract type

Hi,
first i would like to thank you for your cooperation and help ,
please , i would like to know which type of contracts describes the followig sitiuation , ( FP,CR, T&M , OR IT MAY BE OTHER TYPE )
a contract has a specific detemined budget and only allowed to increase by 10% and not to be decreased by 20% , the contractor is payed for that according to the accomplished quantities at site as per ( unit / rate ) system in a monthly certificates including the costs of the materials used in constructions , and some times i have to face some approved changes in scope that makes the final budget of the project is exceeding the contracted budget as per contract limits ,
i need to know which type of contracts do i have and dealing with?
thank you ,