I'll move this to the billing section for you, @vadersgal.
However there is very little you can do from this end, as you are not the account holder. So you can't cancel by simply ringing up.
If you put in an order with another Openreach serviced ISP, that should trigger an email to your ex husband from Talktalk.
It gives him the chance to keep the service (and keep paying the bills) or, if he does nothing, the new service can start with the new company, and so that will be set up in your name.
If you wish to keep the same phone number, be sure to request this at point of sale.
Your ex husband will be billed 30 days ahead as usual this month, which doesn't usually coincide with the end of contract date, so some days on this month's bill may already be at the full price rate, pro rata. Depending on the dates, any overpayment will be refunded to his My Account on the next bill. He can claim that back using the same information as for the Direct Debit, so the DD should be kept in place till all of that is settled.
He'll then get a bill for £0.00, which means that the DD can be safely removed.
He'll be expected to return equipment, which could be tricky in this situation!
If it's not returned, there's a £50 fine.
Staff on here could send a returns bag to your house, once the service has ended, so you should then return equipment.
You won't receive the demand for it from Talktalk, as you are not the account holder, but there is still the responsibility to return the equipment, so perhaps best done by asking staff on the forum.
They will need you to complete your community forum profile. Go via your avatar/name; settings; Personal Information: landline telephone number; SAVE CHANGES.
This will show them your husband's account.
They cannot close the account for you via this forum. Only your ex husband can do that by phoning Talktalk himself or by him not reacting to their prompts to make him stay.
They may not even be able to tell you the precise day the contract ends, as you are not the account holder. There are all sorts of GDPR issues at stake here.
But, at the end of a contract, the service doesn't suddenly just stop, it rolls over at full price. You won't be left with nothing while waiting for a new service to be started up.
Gliwmaeden2, a fellow customer.
