I know of some owners in phase 1 who were not connected to the meter they thought was theirs. aquagest eventually sorted this.
Worth insisiting Aquagest come and check your meter, you must be able to show them previous bills as a comparison.
Could someone have left a tap running somewhere, if no sign of a leak? Could someone link in to outside tap?
They should be able to turn the meter off to check if it is indeed yours, if not satisfied ask them for a complaints form ,all businesses must supply one and visit the OMIC office in San Javier or seek legal advice. as that is not realistic bill if used sensibly