My mobile phone sends everything 5 times!

Hey, guys

I have got a little bit of a problem… The cost for my mobile phone has never been higher than 20 euros a month. However this month a had to pay 100 euros! I looked into that and it appears that every text message was registered 5 times. All of the text messages had the same recipient and date on it. However my recipients have never received my message 5 times… Does anybody know wether the problem is in my mobile phone or with my provider?

Thanks in advance