Gmac Mortgage They found a way to raise a fixed mortgage Ewing, New Jersey

My mortgage company had me at 8.75 from 2003 to this day.I have never missed a payment.In 2009 they saide i missed a peyment in 2006.They asked me for checks from certin months.I sent them and no answer from them.I called and they saide they need the same months but from 2007.I sent them the front and back of the three months they asked for.I recieved no answer.I called and they asked for all of 2007 to dec. 2009 and I paide $72. for all thesse months sent them to them by fax.And they sent me a peyment plan of $1,500. a month tile june more than what was owed.My note was $793. a month.In 2005 I have been peying $820. and $830. at times.They saide they also made a mistake with my escrow amount and I had to pey that also.My house was at a value of $85,000. and is now at $126,000. Seems as though they are just trying to take my home as they have done to three others on this block.What should I do now?