I am afraid to say that this is absolutely typical of this despicable company.
E-mails to terminate your contract are ignored as part of their routine and as for stopping direct debits, Pipex is one of the more infamous in banking circles for breaking the rules on direct debits or charge card withdrawals.
WRITE to them demanding that your account is closed and your account is not debited. Send the letter by recorded delivery and KEEP the proof of posting. Copy the letter to your bank for security as well.
I'm sorry to say that the only way I was able to save my business was to take them to court which I subsequently won but it still took THREE bailiff visits to retrieve the money that they owed me.
Pipex is a bully and a vile company with whom to do business. They provide shoddy service with even worse customer care. Their technical support is worse than useless and yet they charge you a premium rate. OFCOM couldn't give a monkey's and the office of fair trading seems also to be toothless. Customers are treated with total disrespect and I'd be happy to see these [people of doubtful parentage] out of business.
SHARK!