What the hell should i do!!! Women troubles!!!

Seriously confused and don't know what the hell to do. The story goes:

I had a girlfriend, was an ok relationship, didn't feel much for her so we split, and found another girl. Absolutely love this girl, but after a few arguments and her finding out i text another girl (completely innocent) we split up. Now after about 2 weeks, after a whole load of trying, getting told different things, having arguements i had finally found out that my girlfriend does still love me and would want to be with me but can't trust me. She is seeing someone else at the moment but said its only to help forget about me.

Now i'm still kind of trying to get my ex back, by just being her best friend and being there when she's upset or anything. Problem is she is getting phonecalls from strangers saying that i'm back with ex and sleeping with her. Now this doesn't help in my favour of getting my girl back.

I know my ex still likes me so....

1, Is she seriously making phonecalls to my girlfriend just so we will never be together, so maybe she can have me back?

2, Is my girlfriend making it up to try and trick me into saying i have done it? To make the break easier?

Also i could go and ask both, but i don't know how i could get the truth out of both of them without hurting them, or me.

1, If i ask my ex, and possibly threaten her with something (no idea yet lol) and she tells me the truth that nothing has happened and doesn't know anything about phonecalls. How can i then tell my girlfriend that i know she is lying? Because if i mention "i spoke to my ex" she will go mental and think i still like her. Or should i just admit to myself she is making it up, and never know the real reason as to why?

2, If my ex admits it, what should i do? How could i get it to stop? And should i tell my girlfriend that i know who's making them? So she can deal with it? But again that would mean i have spoken to my ex, so again the girlfriend will go mental.


And no i cannot get them both together, as claws will fly and i can't let my ex get beaten up (which she undoubtedly would). But if i helped her, i would get the whole "you still care about her" thing from my girlfriend.

I'm in a pickle :( I just want to prove to my girlfriend she can trust me, but with these phonecalls its not helping me :(

In legal terms phone calls are not probative. They cannot be used in a court of law unless serious court ordered wire tapping is involved.
Also phone calls like the ones you mention are hearsay.
Hearsay is: "I'm telling you that she told me that he was...."
Hearsay is also not probative and usually not allowed in court as evidence of the facts or truth of any matter.
So usually when I hear hearsay I disregard it as gossip.
Anybody who hears hearsay and believes it is the truth should investigate the veracity of the hearsay statement before acting upon it.
A rule I value in relationships is that if it's not a fact or the truth don't say it.
Hearsay is worthless to me on the phone or in person.
Everyone in a relationship should value the truth and facts concerning any deal breaker or relationship ending situation.