VM External Cable Feed in garden to Omnibox on house.

The feed is a co-joined (double) attached cable which I presume is telephone & Internet feed which runs from the street into my garden, upto the junction box fixed on the outside of my house, before it then enters into my property. 

We only use TV & Internet. Telephone not connected. 

When we first signed up to VM we received our internet & TV via a cable 'piggybacking' thru next doors omnibox.  We were unawares. The neighbours were annoyed.  The external cable since then has been independently servicing my property. Which when laid in my garden, leading to my wall socket, it is surface 'mounted' so to speak. In other words, it rests just under the surface if not, on top of my grass.  It is a tad concerning to say the least with dogs that like to chew 'things' such as surface laid cables.

I have now dug a deep(ish) trench in line with where the cable lies with the intention that it can be dropped in the said trench but it needs extending to drop into the void.

Would VM be able to assist in the relocation & extension of this cable bearing in mind I have just re-newed/upgraded my contract..? Or, is it viable for a DIYer to disconnect this cable feed & get a jointer cable to extend the current cable..?  I could also benefit from having a new/replacement Omnibox as my current one is a bit shabby.

Any suggestions & pointers would be most welcome.  Thanks.