The entitlement of statutory maternity benefits for a contract employee is in operation only until the actual expiration date of the contract. It cannot be a reason for further extending the previously fixed contract term.
Regarding your case, based on the information provided from 15-06-2018 to 06-06-2019, your total service period amounts to 356 days. This indicates that your original 89-day contract has been extended three times already. As of the Expected Delivery Date (EDD) on 19-05-2019, you are currently in the third extended period of your contract, which is set to end on 06-06-2019.
Out of the total 26 weeks of maternity benefits, you can take 8 weeks prior to the EDD and the remaining 18 weeks after, provided that the third term of your contract is still valid until 06-06-2019. Therefore, you are eligible for statutory maternity benefits only until 06-06-2019. It is unlikely that your employer will agree to a fourth extension to allow you to fully utilize the benefits.
Thank you.