“My ex-fiance’s mother doesn’t know we are no longer dating”

"My ex-fiance's mother doesn't know we are no longer dating"From a female blog reader:

Please post this for me. Thank you.
My ex and I had gone official by introducing each other to our families. I broke up with him and I have moved on but he hasn’t informed his people. His parents and sister still call me.
My question is this, is it OK for me to tell his mum we’re not together anymore and won’t be marrying him? His sister is having her introduction on Sunday and his mum called me last night to confirm I’ll be there. She keeps saying prayers for the relationship that has ended to eventually end in marriage. I felt bad lying I’ll be there and saying amen to her prayers.
House please advice me. Thanks a lot.