Starting May 2019 I began working on a 6 Months Contract

Good Morning
Starting May 2019 I began working on a 6 Months Contract with DIO.
The Termination clause are as follows:
12. TERMINATION
12.1. Termination of a Client Assignment does not terminate your contract of employment.
12.2. You may not terminate your employment until any current Client Assignment can also be lawfully terminated by us. You may not terminate a Client Assignment without also terminating your contract of employment, without our written agreement. Subject thereto, this employment may be terminated by written notice as follows:
12.2.1. During the first month, either by you or by us with immediate effect
12.2.2. Until you have achieved two years continuous employment, either (a) by you giving us one week’s notice, or (b) by us giving you three weeks’ notice
12.2.3. Thereafter, either (a) by you giving us one week’s notice, or (b) by us giving you notice of two weeks, plus one additional week for each year of continuous employment, up to a maximum of twelve (maximum notice fourteen weeks);
12.3. Your employment will automatically terminate, without any requirement for notice, if continuation of your employment would become unlawful, whether by reason of the expiry of any required work permit, or otherwise.
12.4. Nothing in this section shall prevent us from terminating the employment without notice and without making payment in lieu of notice, where we are justified in so doing.
12.5. If on termination you have taken more or less than the amount of paid leave to which you are entitled (calculated to the date of termination), an adjustment will be made to your final salary payment.
12.6. On termination of your employment for whatever reason, you will forthwith return all property belonging to us or to any Client which is in your possession or under your control. You will if so required by us, confirm in writing that you have complied with your obligation under this term.On 26-Aug-2019 My Contract was Terminated without any Notice stating DIO has failed to receive my (Security Check) SC Clearence yet.However following week upon my enquiring with concerned authority I cam to know my SC clearence has indeed been throu and DIO received the same on 17-Aug-2019.Despite me writing to DIO there has been no reply.I wish to know how I may take up legal action under Breach of Contract.Thanks
Ganesh
JA: Have you discussed the termination with a manager or HR? Or with a lawyer?
Customer: Asked the Agency for reasons but they too have not been provided any except that "My SC clearance has not come through" which is clearly a lie
JA: What is your employment status? Are you an employee, freelancer, consultant or contractor? Do you belong to a union?
Customer: Freelance IT Contractor usually work through my own LTD Company However in the above case since MoD Defence Infrastructure Organisation (DIO) insists to work within IR35 had to be employed through a Payroll company called Danbro
JA: Anything else you want the Lawyer to know before I connect you?
Customer: That my SC Clearance was indeed successful cleared and still valid currently My Mobile No is +44-7721305256